| Message ID | 20230223074826.3782643-1-wangxiongfeng@huaweicloud.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC] blk-mq: avoid housekeeping CPUs scheduling a worker on a non-housekeeping CPU | expand |
On Thu, Feb 23, 2023 at 03:48:26PM +0800, Xiongfeng Wang wrote: > From: Xiongfeng Wang <wangxiongfeng2@huawei.com> > > 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. This looks like an odd non-systemic bandaid. Shouldn't we have a more generic way nothing ever gets onto these non-housekeeping CPUs by making sure they never show up in the cpumask, and never get completion IPIs?
diff --git a/block/blk-mq.c b/block/blk-mq.c index d3494a796ba8..1e84d393cce3 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -21,6 +21,7 @@ #include <linux/llist.h> #include <linux/cpu.h> #include <linux/cache.h> +#include <linux/sched/isolation.h> #include <linux/sched/sysctl.h> #include <linux/sched/topology.h> #include <linux/sched/signal.h> @@ -2245,6 +2246,8 @@ 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; @@ -2255,7 +2258,17 @@ static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async, } } - 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_TYPE_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)); }