On 8/21/2024 10:52 PM, Bart Van Assche wrote:
On 8/21/24 5:29 AM, MANISH PANDEY wrote:
How about introducing a new rq_affinity ( may be rq_affinity = 3) for
using cpus_equal_capacity() using new flag QUEUE_FLAG_SAME_CAPACITY.
if (cpu == rq->mq_ctx->cpu ||
(!test_bit(QUEUE_FLAG_SAME_FORCE, &rq->q->queue_flags) &&
cpus_share_cache(cpu, rq->mq_ctx->cpu) &&
+ (test_bit(QUEUE_FLAG_CPU_CAPACITY, &rq->q->queue_flags))
&& cpus_equal_capacity(cpu, rq->mq_ctx->cpu)))
return false;
Could you please consider raising similar change, if this seems fine
for all.
I'm not sure that a change like the above would be acceptable.
What is the performance impact of the above change? Redirecting
completion interrupts from a slow core to a fast core causes additional
cache misses if the I/O was submitted from a slow core. Are there
perhaps use cases for which the above change slows down I/O?
Thanks,
Bart.
Hi Bart,
> What is the performance impact of the above change?
No impact at all, as we are not changing the logic, we are just
proposing an on/off switch and give flexibility to users. Let the user
choose what's the best for their system.
Intention behind proposing a new flag is like we shouldn't break the
backward compatibility, as the change is also included in stable release
branches.
/* same CPU or cache domain and capacity? Complete locally */
if (cpu == rq->mq_ctx->cpu ||
(!test_bit(QUEUE_FLAG_SAME_FORCE, &rq->q->queue_flags) &&
cpus_share_cache(cpu, rq->mq_ctx->cpu) &&
+ (test_bit(QUEUE_FLAG_CPU_CAPACITY, &rq->q->queue_flags) ||
cpus_equal_capacity(cpu, rq->mq_ctx->cpu))))
return false;
So basically below would act as on/ off switch
QUEUE_FLAG_CPU_CAPACITY - with rq_affinity=1 , it will be clear
- with rq_affinity=3 , it will be set.
Regards
Mansih
