Preemption question (4xx related)
Hi,
Preemption is disabled on the vast majority of powerpc targets. Are there any known problems in this area ? I'd like to enable CONFIG_PREEMPT_VOLUNTARY on AMCC 405EX target, to increase application responsiveness. Is it a bad idea ?
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Quoted 7 lines · Felix Radensky
Hi,
Preemption is disabled on the vast majority of powerpc targets. Are there any known problems in this area ? I'd like to enable
CONFIG_PREEMPT_VOLUNTARYon AMCC 405EX target, to increase application responsiveness. Is it a bad idea ?
In theory it should work, but as you may have noticed, it's generally disabled and thus not very well tested.
It would be a good idea for us, some of the core devs, to turn that on in our usual test configs in fact.
Cheers,
Ben.
Quoted 9 lines · Benjamin Herrenschmidt
Quoted 7 lines · Felix Radensky
Hi,
Preemption is disabled on the vast majority of powerpc targets. Are there any known problems in this area ? I'd like to enable
CONFIG_PREEMPT_VOLUNTARYon AMCC 405EX target, to increase application responsiveness. Is it a bad idea ?
Quoted 5 lines
In theory it should work, but as you may have noticed, it's generally disabled and thus not very well tested.
It would be a good idea for us, some of the core devs, to turn that on in our usual test configs in fact.
I've toyed with that idea myself. I keep coming back to the fact that you need a workload that would really leverage it, and I don't have one at the moment.
josh
Quoted 2 lines · Josh Boyer
I've toyed with that idea myself. I keep coming back to the fact that you need a workload that would really leverage it, and I don't have one at the moment.
To some extent that's true but just turning full preemption including kernel side with all the associated debug bits and lockdep should make a whole bunch of things show up even with ordinary workloads.
For 440 tend to boot an ubuntu distro off NFS root with all X & DRI 3D etc... and then run compiz :-)
Cheers,
Ben.
Quoted 8 lines · Benjamin Herrenschmidt
Quoted 2 lines · Josh Boyer
I've toyed with that idea myself. I keep coming back to the fact that you need a workload that would really leverage it, and I don't have one at the moment.
To some extent that's true but just turning full preemption including kernel side with all the associated debug bits and lockdep should make a whole bunch of things show up even with ordinary workloads.
I can look at doing that for ppc44x_defconfig. I'll be honest and say I don't expect it to go well, particularly with lockdep :).
Quoted 2 lines
For 440 tend to boot an ubuntu distro off NFS root with all X & DRI 3D etc... and then run compiz :-)
Yes. Because that's a totally realistic workload for a 440. I'm surprised you don't have a p595 machine acting as your home router too! ;)
josh
Quoted 10 lines · Josh Boyer
Quoted 8 lines · Benjamin Herrenschmidt
Quoted 2 lines · Josh Boyer
I've toyed with that idea myself. I keep coming back to the fact that you need a workload that would really leverage it, and I don't have one at the moment.
To some extent that's true but just turning full preemption including kernel side with all the associated debug bits and lockdep should make a whole bunch of things show up even with ordinary workloads.
Quoted 8 lines
I can look at doing that for
ppc44x_defconfig. I'll be honest and say I don't expect it to go well, particularly with lockdep :).Quoted 2 lines
For 440 tend to boot an ubuntu distro off NFS root with all X & DRI 3D etc... and then run compiz :-)
Yes. Because that's a totally realistic workload for a 440. I'm surprised you don't have a p595 machine acting as your home router too! ;)
It doesn't need to be realistic. In fact, a "realistic" workload is the worst thing to test with because it won't exercise all the "uncommon" code path which are the ones likely to bite.
So yesm it's not a "realistic" workload, but it's a good "torture" workload to find bugs.
Cheers,
Ben.
Quoted 20 lines · Benjamin Herrenschmidt
Quoted 10 lines · Josh Boyer
Quoted 8 lines · Benjamin Herrenschmidt
Quoted 2 lines · Josh Boyer
I've toyed with that idea myself. I keep coming back to the fact that you need a workload that would really leverage it, and I don't have one at the moment.
To some extent that's true but just turning full preemption including kernel side with all the associated debug bits and lockdep should make a whole bunch of things show up even with ordinary workloads.
Quoted 8 lines
I can look at doing that for
ppc44x_defconfig. I'll be honest and say I don't expect it to go well, particularly with lockdep :).Quoted 2 lines
For 440 tend to boot an ubuntu distro off NFS root with all X & DRI 3D etc... and then run compiz :-)
Yes. Because that's a totally realistic workload for a 440. I'm surprised you don't have a p595 machine acting as your home router too! ;)
Quoted 6 lines
It doesn't need to be realistic. In fact, a "realistic" workload is the worst thing to test with because it won't exercise all the "uncommon" code path which are the ones likely to bite.
So yesm it's not a "realistic" workload, but it's a good "torture" workload to find bugs.
It was a joke. But yes, you make perfectly valid points :)
josh
Quoted 8 lines · Benjamin Herrenschmidt
Quoted 7 lines · Felix Radensky
Hi,
=20
Preemption is disabled on the vast majority of powerpc targets. Are there any known problems in this area ? I'd like to enableCONFIG_PREEMPT_VOLUNTARYon AMCC 405EX target, to increase application responsiveness. Is it a bad idea ?
Quoted 6 lines
=20
In theory it should work, but as you may have noticed, it's generally disabled and thus not very well tested.
=20
It would be a good idea for us, some of the core devs, to turn that on in our usual test configs in fact.
FWIW, on my PowerBook I've been running with CONFIG_PREEMPT_VOLUNTARY enabled for a long time (more than a year). No problems so far, and it definitely seems to help a lot for interactivity.
--=20
Earthling Michel D=C3=A4nzer | http://www.vmware.c=
om
Libre software enthusiast | Debian, X and DRI developer