relay: add relay_reserve_cpu()
RFC PATCH 4/6 relay: add relay_reserve_cpu()
This patch adds the ability to explicitly specify the per-cpu buffer to reserve space in. Needed for early DTI tracing.
--- relay.h | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+)
include/linux/relay.h +33 -0
@@ -269,6 +269,39 @@ static inline void *relay_reserve(struct rchan *chan, size_t length) }/** +* relay_reserve_cpu - reserve slot in given cpu's channel buffer +* @chan: relay channel +* @length: number of bytes to reserve +* @cpu: cpu to log to +* +* Returns pointer to reserved slot, NULL if full. +* +* Reserves a slot in the given cpu's channel buffer. +* Does not protect the buffer at all - caller must provide +* appropriate synchronization. +* +* NOTE: this is almost certainly not the function you want - +* use relay_reserve() instead for normal logging. This version +* is specialized for things like early tracing. +*/ +static inline void *relay_reserve_cpu (struct rchan *chan,size_t length, +unsigned int cpu) +{ +void *reserved; +struct rchan_buf *buf = chan->buf[cpu]; + +if (unlikely (buf->offset + length > buf->chan->subbuf_size)) { + length =relay_switch_subbuf (buf, length); +if (!length) +return NULL ; + } + reserved = buf->data + buf->offset; + buf->offset += length; + +return reserved; +} + +/** * subbuf_start_reserve - reserve bytes at the start of a sub-buffer * @buf: relay channel buffer * @length: number of bytes to reserve
Quoted 3 lines · * Tom Zanussi ([email protected]) wrote:
This patch adds the ability to explicitly specify the per-cpu buffer to reserve space in. Needed for early DTI tracing.
This should come with the ability to tell relay where the already allocated static buffers are. Can you tell me a little more on why the standard relay_reserve would not do the job? Is smp_processor_id() not ready to output a sensible CPU id yet ?
Quoted 59 lines
Signed-off-by Tom Zanussi <[email protected]>Signed-off-by David Wilder <[email protected]>--- relay.h | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+)include/linux/relay.h +33
-1@@ -269,6 +269,39 @@ static inline void *relay_reserve(struct rchan *chan, size_t length) }/** +* relay_reserve_cpu - reserve slot in given cpu's channel buffer +* @chan: relay channel +* @length: number of bytes to reserve +* @cpu: cpu to log to +* +* Returns pointer to reserved slot, NULL if full. +* +* Reserves a slot in the given cpu's channel buffer. +* Does not protect the buffer at all - caller must provide +* appropriate synchronization. +* +* NOTE: this is almost certainly not the function you want - +* use relay_reserve() instead for normal logging. This version +* is specialized for things like early tracing. +*/ +static inline void *relay_reserve_cpu (struct rchan *chan,size_t length, +unsigned int cpu) +{ +void *reserved; +struct rchan_buf *buf = chan->buf[cpu]; + +if (unlikely (buf->offset + length > buf->chan->subbuf_size)) { + length =relay_switch_subbuf (buf, length); +if (!length) +return NULL ; + } + reserved = buf->data + buf->offset; + buf->offset += length; + +return reserved; +} + +/** * subbuf_start_reserve - reserve bytes at the start of a sub-buffer * @buf: relay channel buffer * @length: number of bytes to reserve -To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected]
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Signature · 3 lines
Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
Quoted 10 lines · Mathieu Desnoyers
Quoted 3 lines · * Tom Zanussi ([email protected]) wrote:
This patch adds the ability to explicitly specify the per-cpu buffer to reserve space in. Needed for early DTI tracing.
This should come with the ability to tell relay where the already allocated static buffers are. Can you tell me a little more on why the standard
relay_reservewould not do the job? Issmp_processor_id()not ready to output a sensible CPU id yet ?
In the case of early tracing, the DTI code uses a global buffer and saves the cpuid along with each event. Later, when the relay channel is available, the relogging code wants to put each event in the appropriate per-cpu relay buffer. The standard relay_reserve() always uses the current cpuid, rather than the cpuid attached to the event, which is not what we want. relay_reserve_cpu() simply allows a cpuid other than the current one to be used.
Tom