Hi Frederic,
Sorry to disturb you. It's just that I think you may be interested in this
patch. I notice you are reviewing some other CPU isolation patches. Appreciate
it a lot if you can give it a look. Or just ignore it if you are not interested.
Thanks,
Xiongfeng
On 2022/2/10 17:35, Xiongfeng Wang wrote:
> When NOHZ_FULL is enabled, such as in HPC situation, CPUs are divided
> into housekeeping CPUs and non-housekeeping CPUs. Non-housekeeping CPUs
> are NOHZ_FULL CPUs and are often monopolized by the userspace process,
> such HPC application process. Any sort of interruption is not expected.
>
> blk_mq_hctx_next_cpu() selects each cpu in 'hctx->cpumask' alternately
> to schedule the work thread blk_mq_run_work_fn(). When 'hctx->cpumask'
> contains housekeeping CPU and non-housekeeping CPU at the same time, a
> housekeeping CPU, which want to request a IO, may schedule a worker on a
> non-housekeeping CPU. This may affect the performance of the userspace
> application running on non-housekeeping CPUs.
>
> So let's just schedule the worker thread on the current CPU when the
> current CPU is housekeeping CPU.
>
> Signed-off-by: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
> ---
> block/blk-mq.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 1adfe4824ef5..ff9a4bf16858 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -24,6 +24,7 @@
> #include <linux/sched/sysctl.h>
> #include <linux/sched/topology.h>
> #include <linux/sched/signal.h>
> +#include <linux/sched/isolation.h>
> #include <linux/delay.h>
> #include <linux/crash_dump.h>
> #include <linux/prefetch.h>
> @@ -2036,6 +2037,8 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
> static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
> unsigned long msecs)
> {
> + int work_cpu;
> +
> if (unlikely(blk_mq_hctx_stopped(hctx)))
> return;
>
> @@ -2050,7 +2053,17 @@ static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
> put_cpu();
> }
>
> - kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work,
> + /*
> + * Avoid housekeeping CPUs scheduling a worker on a non-housekeeping
> + * CPU
> + */
> + if (tick_nohz_full_enabled() && housekeeping_cpu(smp_processor_id(),
> + HK_FLAG_WQ))
> + work_cpu = smp_processor_id();
> + else
> + work_cpu = blk_mq_hctx_next_cpu(hctx);
> +
> + kblockd_mod_delayed_work_on(work_cpu, &hctx->run_work,
> msecs_to_jiffies(msecs));
> }
>
>
