Add NAPI support to ll_temac driver
Subsystems (2)
Hi,
I would like to try to add NAPI support for ll_temac and look if help us to improve performance on Microblaze system. I would expect that bandwidth should be increased. We have the second non mainline driver which use tasklets and it provides better
performance than mainline driver but not so big that's why I think that NAPI
can increase performance.
Can you please point me to any driver which I could use as a template? Or any developer guide to do so.
Do you know any other option how to improve driver performance on low speed cpu?
I have found that driver spends a lot of time on skb allocation and preallocated SKBs help a little bit. I have done a test where I increased number of preallocated BDs(SKBs) for rx to 35000 and disable new BD(SKB) allocation in rx_irq. 35000 BDs is setup because I need them to successfully finish netperf test. I have got 25% bandwidth increasing.
It will be also nice to be able to allocate several BDs(SKBs) which could be faster than allocate them in sequence.
Thanks,
Michal
Signature · 4 lines
Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/ Microblaze U-BOOT custodian
Quoted 14 lines · Michal Simek
Hi,
I would like to try to add NAPI support for
ll_temacand look if help us to improve performance on Microblaze system. I would expect that bandwidth should be increased.
We have the second non mainline driver which use tasklets and it provides better
performance than mainline driver but not so big that's why I think that NAPI
can increase performance.Can you please point me to any driver which I could use as a template? Or any developer guide to do so.
Do you know any other option how to improve driver performance on low speed cpu?
Quoted 8 lines
I have found that driver spends a lot of time on skb allocation and preallocated SKBs help a little bit. I have done a test where I increased number of preallocated BDs(SKBs) for rx to 35000 and disable new BD(SKB) allocation in
rx_irq. 35000 BDs is setup because I need them to successfully finish netperf test. I have got 25% bandwidth increasing.It will be also nice to be able to allocate several BDs(SKBs) which could be faster than allocate them in sequence.
Depends if your cpu has some cache. The best performance is to try to get high cache hit ratios.
One possible way to get better performance is to change driver to allocate skbs only right before calling netif_rx(), so that you dont have to access cold sk_buff data twice (once when allocating skb and put it in ring buffer, a second time when receiving frame)
drivers/net/niu.c is a good example for this (NAPI + netdev_alloc_skb() just in time + pull in skbhead only first cache line of packet)
drivers/net/ftmac100.c is also a recent driver (and probably a better start with less complex hardware than NIU) using these tricks
{ skb = netdev_alloc_skb_ip_align(netdev, 128);
__pskb_pull_tail(skb, min(length, 64));
}
On Tue, 2011-04-19 at 12:43 +0200, Eric Dumazet wrote:
[...]
Quoted 7 lines
One possible way to get better performance is to change driver to allocate skbs only right before calling
netif_rx(), so that you dont have to access coldsk_buffdata twice (once when allocating skb and put it in ring buffer, a second time when receiving frame)
drivers/net/niu.cis a good example for this (NAPI +netdev_alloc_skb()just in time + pull in skbhead only first cache line of packet)
[...]
If the hardware can do RX checksumming (it's not clear) then the driver should pass the paged buffers into GRO and that will take care of skb allocation as necessary.
Ben.
Signature · 3 lines
Ben Hutchings, Senior Software Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.
Quoted 7 lines · Ben Hutchings
On Tue, 2011-04-19 at 12:43 +0200, Eric Dumazet wrote:
[...]Quoted 5 lines
One possible way to get better performance is to change driver to allocate skbs only right before calling
netif_rx(), so that you dont have to access coldsk_buffdata twice (once when allocating skb and put it in ring buffer, a second time when receiving frame)
Quoted 7 lines
Quoted 2 lines
drivers/net/niu.cis a good example for this (NAPI +netdev_alloc_skb()just in time + pull in skbhead only first cache line of packet)[...]
If the hardware can do RX checksumming (it's not clear) then the driver should pass the paged buffers into GRO and that will take care of skb allocation as necessary.
Hardware supports RX and TX partial checksumming. I can enable it. The driver has also this option and from my tests there is of course some performance improvemetn.
Just for sure - here are links on documentation.
http://www.xilinx.com/support/documentation/ip_documentation/xps_ll_temac.pdf
or
http://www.xilinx.com/support/documentation/ip_documentation/axi_ethernet/v2_01_a/ds759_axi_ethernet.pdf
About SKB allocation. I fixed our non mainline driver to allocate skb based on current mtu size. Mainline driver allocate max mtu (9k). This has also impact on performance because Microblaze works with smaller SKBs.
Can you please be more specific about passing the paged buffers into GRO? Or point me to any documentation or code which can help me to understand what that means.
Thanks,
Michal
Signature · 4 lines
Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/ Microblaze U-BOOT custodian
Quoted 3 lines · Michal Simek
Can you please be more specific about passing the paged buffers into GRO? Or point me to any documentation or code which can help me to understand what that means.
Search for napi_get_frags() :
drivers/net/mlx4/en_rx.c:597: struct sk_buff *gro_skb = napi_get_frags(&cq->napi);drivers/net/cxgb3/sge.c:2091: skb = napi_get_frags(&qs->napi);drivers/net/cxgb4/sge.c:1517: skb = napi_get_frags(&rxq->rspq.napi);drivers/net/qlge/qlge_main.c:1484: skb = napi_get_frags(napi);drivers/net/sfc/rx.c:471: skb = napi_get_frags(napi);drivers/net/benet/be_main.c:1039: skb = napi_get_frags(&eq_obj->napi);drivers/net/cxgb4vf/sge.c:1479: skb = napi_get_frags(&rxq->rspq.napi);
Quoted 16 lines · Michal Simek
Quoted 7 lines · Ben Hutchings
On Tue, 2011-04-19 at 12:43 +0200, Eric Dumazet wrote:
[...]Quoted 5 lines
One possible way to get better performance is to change driver to allocate skbs only right before calling
netif_rx(), so that you dont have to access coldsk_buffdata twice (once when allocating skb and put it in ring buffer, a second time when receiving frame)Quoted 7 lines
Quoted 2 lines
drivers/net/niu.cis a good example for this (NAPI +netdev_alloc_skb()just in time + pull in skbhead only first cache line of packet)[...]
If the hardware can do RX checksumming (it's not clear) then the driver should pass the paged buffers into GRO and that will take care of skb allocation as necessary.
Quoted 8 lines
Hardware supports RX and TX partial checksumming. I can enable it. The driver has also this option and from my tests there is of course some performance improvemetn.
Just for sure - here are links on documentation.
http://www.xilinx.com/support/documentation/ip_documentation/xps_ll_temac.pdf
or
http://www.xilinx.com/support/documentation/ip_documentation/axi_ethernet/v2_01_a/ds759_axi_ethernet.pdf
I'm not going to read those. Just providing brief advice.
Quoted 7 lines
About SKB allocation. I fixed our non mainline driver to allocate skb based on current mtu size. Mainline driver allocate max mtu (9k). This has also impact on performance because Microblaze works with smaller SKBs.
Can you please be more specific about passing the paged buffers into GRO? Or point me to any documentation or code which can help me to understand what that means.
You would use napi_get_frags() to get a new or recycled skb, fill in skb->frags, then call napi_gro_frags() to pass it into GRO. The benet, cxgb3 and sfc drivers do this.
Ben.
Signature · 3 lines
Ben Hutchings, Senior Software Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.
Quoted 25 lines · Ben Hutchings
Quoted 15 lines · Michal Simek
Quoted 7 lines · Ben Hutchings
On Tue, 2011-04-19 at 12:43 +0200, Eric Dumazet wrote:
[...]Quoted 5 lines
One possible way to get better performance is to change driver to allocate skbs only right before calling
netif_rx(), so that you dont have to access coldsk_buffdata twice (once when allocating skb and put it in ring buffer, a second time when receiving frame)Quoted 7 lines
Quoted 2 lines
drivers/net/niu.cis a good example for this (NAPI +netdev_alloc_skb()just in time + pull in skbhead only first cache line of packet)[...]
If the hardware can do RX checksumming (it's not clear) then the driver should pass the paged buffers into GRO and that will take care of skb allocation as necessary.
Quoted 6 lines
Hardware supports RX and TX partial checksumming. I can enable it. The driver has also this option and from my tests there is of course some performance improvemetn.
Just for sure - here are links on documentation.
http://www.xilinx.com/support/documentation/ip_documentation/xps_ll_temac.pdf
or
http://www.xilinx.com/support/documentation/ip_documentation/axi_ethernet/v2_01_a/ds759_axi_ethernet.pdfI'm not going to read those. Just providing brief advice.
Quoted 8 lines
Quoted 4 lines
About SKB allocation. I fixed our non mainline driver to allocate skb based on current mtu size. Mainline driver allocate max mtu (9k). This has also impact on performance because Microblaze works with smaller SKBs.
Can you please be more specific about passing the paged buffers into GRO? Or point me to any documentation or code which can help me to understand what that means.
You would use
napi_get_frags()to get a new or recycled skb, fill inskb->frags, then callnapi_gro_frags()to pass it into GRO. The benet, cxgb3 and sfc drivers do this.
ok. Will look.
Thanks,
Michal
Signature · 4 lines
Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/ Microblaze U-BOOT custodian
Hi,
Quoted 25 lines · Ben Hutchings
Quoted 15 lines · Michal Simek
Quoted 7 lines · Ben Hutchings
On Tue, 2011-04-19 at 12:43 +0200, Eric Dumazet wrote:
[...]Quoted 5 lines
One possible way to get better performance is to change driver to allocate skbs only right before calling
netif_rx(), so that you dont have to access coldsk_buffdata twice (once when allocating skb and put it in ring buffer, a second time when receiving frame)Quoted 7 lines
Quoted 2 lines
drivers/net/niu.cis a good example for this (NAPI +netdev_alloc_skb()just in time + pull in skbhead only first cache line of packet)[...]
If the hardware can do RX checksumming (it's not clear) then the driver should pass the paged buffers into GRO and that will take care of skb allocation as necessary.
Quoted 6 lines
Hardware supports RX and TX partial checksumming. I can enable it. The driver has also this option and from my tests there is of course some performance improvemetn.
Just for sure - here are links on documentation.
http://www.xilinx.com/support/documentation/ip_documentation/xps_ll_temac.pdf
or
http://www.xilinx.com/support/documentation/ip_documentation/axi_ethernet/v2_01_a/ds759_axi_ethernet.pdfI'm not going to read those. Just providing brief advice.
Quoted 8 lines
Quoted 4 lines
About SKB allocation. I fixed our non mainline driver to allocate skb based on current mtu size. Mainline driver allocate max mtu (9k). This has also impact on performance because Microblaze works with smaller SKBs.
Can you please be more specific about passing the paged buffers into GRO? Or point me to any documentation or code which can help me to understand what that means.
You would use
napi_get_frags()to get a new or recycled skb, fill inskb->frags, then callnapi_gro_frags()to pass it into GRO. The benet, cxgb3 and sfc drivers do this.
I have measured TX path and I have found that driver design is not so good.
It is always create one BD for one SKB and it starts DMA to copy packet to controller and send it. On 66MHz cpu it takes approximately 800 cpu cycles (not 800 instructions) for sending (1.5k packet). Current driver also enable irq for TX and when the packet is send interrupt is generated and skb is freed.
I see that it takes more time to handle the IRQ than busy waiting when DMA is done. I looked at sfc driver and there is any TX queue and any notifier. Hos does it work? Is it required to have any hw support?
Thanks,
Michal
Signature · 4 lines
Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/ Microblaze U-BOOT custodian
On Wed, 2011-04-20 at 13:06 +0200, Michal Simek wrote:
[...]
Quoted 3 lines
I have measured TX path and I have found that driver design is not so good. It is always create one BD for one SKB and it starts DMA to copy packet to controller and send it.
You will always get a single packet at a time to push to the hardware. The only improvement you can make on this is to implement segmentation offload, but if the hardware doesn't do this then... well, it's not easy.
Quoted 7 lines
On 66MHz cpu it takes approximately 800 cpu cycles (not
800 instructions) for sending (1.5k packet).
Current driver also enable irq for TX and when the packet is send interrupt is generated and skb is freed.
I see that it takes more time to handle the IRQ than busy waiting when DMA is done. I looked at sfc driver and there is any TX queue and any notifier. Hos does it work? Is it required to have any hw support?
The principle of NAPI is that once you receive an IRQ you mask it and poll until there are no more completions to handle. So it greatly reduces this IRQ overhead.
Ben.
Signature · 3 lines
Ben Hutchings, Senior Software Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.
Quoted 4 lines · Michal Simek
About SKB allocation. I fixed our non mainline driver to allocate skb based on current mtu size. Mainline driver allocate max mtu (9k). This has also impact on performance because Microblaze works with smaller SKBs.
Make sure it wont crash/freeze if some evil guy sends a big frame
Quoted 11 lines · Eric Dumazet
Quoted 10 lines · Michal Simek
Hi,
I would like to try to add NAPI support for
ll_temacand look if help us to improve performance on Microblaze system. I would expect that bandwidth should be increased. We have the second non mainline driver which use tasklets and it provides better
performance than mainline driver but not so big that's why I think that NAPI
can increase performance.Can you please point me to any driver which I could use as a template? Or any developer guide to do so.
Quoted 8 lines
Quoted 5 lines
Do you know any other option how to improve driver performance on low speed cpu?
I have found that driver spends a lot of time on skb allocation and preallocated SKBs help a little bit. I have done a test where I increased number of preallocated BDs(SKBs) for rx to 35000 and disable new BD(SKB) allocation in
rx_irq. 35000 BDs is setup because I need them to successfully finish netperf test. I have got 25% bandwidth increasing.It will be also nice to be able to allocate several BDs(SKBs) which could be faster than allocate them in sequence.
Depends if your cpu has some cache. The best performance is to try to get high cache hit ratios.
Yes it has icache and dcache (write-back or write-through).
Quoted 5 lines
One possible way to get better performance is to change driver to allocate skbs only right before calling
netif_rx(), so that you dont have to access coldsk_buffdata twice (once when allocating skb and put it in ring buffer, a second time when receiving frame)
ok. But I need to allocate BD for dma with pointer to skb where dma should copy data to. I could do it in irq but I would have to wait till dma copy data from ethernet controller to memory. I haven't measure how slow/fast is that copying.
Quoted 10 lines
drivers/net/niu.cis a good example for this (NAPI +netdev_alloc_skb()just in time + pull in skbhead only first cache line of packet)
drivers/net/ftmac100.cis also a recent driver (and probably a better start with less complex hardware than NIU) using these tricks{ skb =
netdev_alloc_skb_ip_align(netdev, 128);
__pskb_pull_tail(skb, min(length, 64));
}
I have change rx for napi but need to debug it a little bit. It works for some packets but I am not able to run any test right now.
Thanks,
Michal
Signature · 4 lines
Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/ Microblaze U-BOOT custodian