Messages in this thread | | | Date | Thu, 6 Jul 2023 15:07:35 +0200 | From | Christoph Hellwig <> | Subject | Re: [PATCH v2 1/4] blk-mq: use percpu csd to remote complete instead of per-rq csd |
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On Thu, Jun 29, 2023 at 07:03:56PM +0800, chengming.zhou@linux.dev wrote: > From: Chengming Zhou <zhouchengming@bytedance.com> > > If request need to be completed remotely, we insert it into percpu llist, > and smp_call_function_single_async() if llist is empty previously. > > We don't need to use per-rq csd, percpu csd is enough. And the size of > struct request is decreased by 24 bytes. > > This way is cleaner, and looks correct, given block softirq is guaranteed to be > scheduled to consume the list if one new request is added to this percpu list, > either smp_call_function_single_async() returns -EBUSY or 0.
Please trim your commit logs to 73 characters per line so that they are readable in git log output.
> static void blk_mq_request_bypass_insert(struct request *rq, > @@ -1156,13 +1157,13 @@ static void blk_mq_complete_send_ipi(struct request *rq) > { > struct llist_head *list; > unsigned int cpu; > + call_single_data_t *csd; > > cpu = rq->mq_ctx->cpu; > list = &per_cpu(blk_cpu_done, cpu); > - if (llist_add(&rq->ipi_list, list)) { > - INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq); > - smp_call_function_single_async(cpu, &rq->csd); > - } > + csd = &per_cpu(blk_cpu_csd, cpu); > + if (llist_add(&rq->ipi_list, list)) > + smp_call_function_single_async(cpu, csd); > }
No need for the list and csd variables here as they are only used once.
But I think this code has a rpboem when it is preemptd between the llist_add and smp_call_function_single_async. We either need a get_cpu/put_cpu around them, or instroduce a structure with the list and csd, and then you can use one pointer from per_cpu and still ensure the list and csd are for the same CPU.
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