From 54a91f3bb9b96ed86bc12b2f7e06b3fce8e86503 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Tue, 10 Sep 2019 09:15:04 -0600 Subject: [PATCH] io_uring: limit parallelism of buffered writes All the popular filesystems need to grab the inode lock for buffered writes. With io_uring punting buffered writes to async context, we observe a lot of contention with all workers hamming this mutex. For buffered writes, we generally don't need a lot of parallelism on the submission side, as the flushing will take care of that for us. Hence we don't need a deep queue on the write side, as long as we can safely punt from the original submission context. Add a workqueue with a limit of 2 that we can use for buffered writes. This greatly improves the performance and efficiency of higher queue depth buffered async writes with io_uring. Reported-by: Andres Freund Signed-off-by: Jens Axboe --- fs/io_uring.c | 47 +++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 39 insertions(+), 8 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 41840bf..03fcd97 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -203,7 +203,7 @@ struct io_ring_ctx { } ____cacheline_aligned_in_smp; /* IO offload */ - struct workqueue_struct *sqo_wq; + struct workqueue_struct *sqo_wq[2]; struct task_struct *sqo_thread; /* if using sq thread polling */ struct mm_struct *sqo_mm; wait_queue_head_t sqo_wait; @@ -446,7 +446,19 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx) static inline void io_queue_async_work(struct io_ring_ctx *ctx, struct io_kiocb *req) { - queue_work(ctx->sqo_wq, &req->work); + int rw; + + switch (req->submit.sqe->opcode) { + case IORING_OP_WRITEV: + case IORING_OP_WRITE_FIXED: + rw = !(req->rw.ki_flags & IOCB_DIRECT); + break; + default: + rw = 0; + break; + } + + queue_work(ctx->sqo_wq[rw], &req->work); } static void io_commit_cqring(struct io_ring_ctx *ctx) @@ -2634,11 +2646,15 @@ static void io_sq_thread_stop(struct io_ring_ctx *ctx) static void io_finish_async(struct io_ring_ctx *ctx) { + int i; + io_sq_thread_stop(ctx); - if (ctx->sqo_wq) { - destroy_workqueue(ctx->sqo_wq); - ctx->sqo_wq = NULL; + for (i = 0; i < ARRAY_SIZE(ctx->sqo_wq); i++) { + if (ctx->sqo_wq[i]) { + destroy_workqueue(ctx->sqo_wq[i]); + ctx->sqo_wq[i] = NULL; + } } } @@ -2846,16 +2862,31 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx, } /* Do QD, or 2 * CPUS, whatever is smallest */ - ctx->sqo_wq = alloc_workqueue("io_ring-wq", WQ_UNBOUND | WQ_FREEZABLE, + ctx->sqo_wq[0] = alloc_workqueue("io_ring-wq", + WQ_UNBOUND | WQ_FREEZABLE, min(ctx->sq_entries - 1, 2 * num_online_cpus())); - if (!ctx->sqo_wq) { + if (!ctx->sqo_wq[0]) { + ret = -ENOMEM; + goto err; + } + + /* + * This is for buffered writes, where we want to limit the parallelism + * due to file locking in file systems. As "normal" buffered writes + * should parellelize on writeout quite nicely, limit us to having 2 + * pending. This avoids massive contention on the inode when doing + * buffered async writes. + */ + ctx->sqo_wq[1] = alloc_workqueue("io_ring-write-wq", + WQ_UNBOUND | WQ_FREEZABLE, 2); + if (!ctx->sqo_wq[1]) { ret = -ENOMEM; goto err; } return 0; err: - io_sq_thread_stop(ctx); + io_finish_async(ctx); mmdrop(ctx->sqo_mm); ctx->sqo_mm = NULL; return ret; -- 2.7.4