Return-Path: Received: from mail-it0-f65.google.com ([209.85.214.65]:33880 "EHLO mail-it0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933186AbdGKVxy (ORCPT ); Tue, 11 Jul 2017 17:53:54 -0400 Received: by mail-it0-f65.google.com with SMTP id o202so533679itc.1 for ; Tue, 11 Jul 2017 14:53:54 -0700 (PDT) From: Trond Myklebust To: anna.schumaker@netapp.com Cc: linux-nfs@vger.kernel.org Subject: [PATCH] NFS: Don't run wake_up_bit() when nobody is waiting... Date: Tue, 11 Jul 2017 17:53:48 -0400 Message-Id: <20170711215348.18596-1-trond.myklebust@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: "perf lock" shows fairly heavy contention for the bit waitqueue locks when doing an I/O heavy workload. Use a bit to tell whether or not there has been contention for a lock so that we can optimise away the bit waitqueue options in those cases. Signed-off-by: Trond Myklebust --- fs/nfs/pagelist.c | 17 ++++++++++++++++- include/linux/nfs_page.h | 2 ++ 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c index ce5f8d2875ae..046162b79b4b 100644 --- a/fs/nfs/pagelist.c +++ b/fs/nfs/pagelist.c @@ -155,9 +155,12 @@ nfs_page_group_lock(struct nfs_page *req, bool nonblock) if (!test_and_set_bit(PG_HEADLOCK, &head->wb_flags)) return 0; - if (!nonblock) + if (!nonblock) { + set_bit(PG_CONTENDED1, &head->wb_flags); + smp_mb__after_atomic(); return wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK, TASK_UNINTERRUPTIBLE); + } return -EAGAIN; } @@ -175,6 +178,10 @@ nfs_page_group_lock_wait(struct nfs_page *req) WARN_ON_ONCE(head != head->wb_head); + if (!test_bit(PG_HEADLOCK, &head->wb_flags)) + return; + set_bit(PG_CONTENDED1, &head->wb_flags); + smp_mb__after_atomic(); wait_on_bit(&head->wb_flags, PG_HEADLOCK, TASK_UNINTERRUPTIBLE); } @@ -193,6 +200,8 @@ nfs_page_group_unlock(struct nfs_page *req) smp_mb__before_atomic(); clear_bit(PG_HEADLOCK, &head->wb_flags); smp_mb__after_atomic(); + if (!test_bit(PG_CONTENDED1, &head->wb_flags)) + return; wake_up_bit(&head->wb_flags, PG_HEADLOCK); } @@ -383,6 +392,8 @@ void nfs_unlock_request(struct nfs_page *req) smp_mb__before_atomic(); clear_bit(PG_BUSY, &req->wb_flags); smp_mb__after_atomic(); + if (!test_bit(PG_CONTENDED2, &req->wb_flags)) + return; wake_up_bit(&req->wb_flags, PG_BUSY); } @@ -465,6 +476,10 @@ void nfs_release_request(struct nfs_page *req) int nfs_wait_on_request(struct nfs_page *req) { + if (!test_bit(PG_BUSY, &req->wb_flags)) + return 0; + set_bit(PG_CONTENDED2, &req->wb_flags); + smp_mb__after_atomic(); return wait_on_bit_io(&req->wb_flags, PG_BUSY, TASK_UNINTERRUPTIBLE); } diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h index abbee2d15dce..d67b67ae6c8b 100644 --- a/include/linux/nfs_page.h +++ b/include/linux/nfs_page.h @@ -33,6 +33,8 @@ enum { PG_UPTODATE, /* page group sync bit in read path */ PG_WB_END, /* page group sync bit in write path */ PG_REMOVE, /* page group sync bit in write path */ + PG_CONTENDED1, /* Is someone waiting for a lock? */ + PG_CONTENDED2, /* Is someone waiting for a lock? */ }; struct nfs_inode; -- 2.13.0