From owner-svn-src-all@freebsd.org Thu Feb 6 20:32:54 2020 Return-Path: Delivered-To: svn-src-all@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 39148239FAA; Thu, 6 Feb 2020 20:32:54 +0000 (UTC) (envelope-from mav@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 48D99L0N4Rz4f0j; Thu, 6 Feb 2020 20:32:53 +0000 (UTC) (envelope-from mav@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id DAB49215FD; Thu, 6 Feb 2020 20:32:53 +0000 (UTC) (envelope-from mav@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 016KWrSD089710; Thu, 6 Feb 2020 20:32:53 GMT (envelope-from mav@FreeBSD.org) Received: (from mav@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 016KWrhr089709; Thu, 6 Feb 2020 20:32:53 GMT (envelope-from mav@FreeBSD.org) Message-Id: <202002062032.016KWrhr089709@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: mav set sender to mav@FreeBSD.org using -f From: Alexander Motin Date: Thu, 6 Feb 2020 20:32:53 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r357639 - in head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs: . sys X-SVN-Group: head X-SVN-Commit-Author: mav X-SVN-Commit-Paths: in head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs: . sys X-SVN-Commit-Revision: 357639 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 06 Feb 2020 20:32:54 -0000 Author: mav Date: Thu Feb 6 20:32:53 2020 New Revision: 357639 URL: https://svnweb.freebsd.org/changeset/base/357639 Log: Reduce number of atomic_add() calls in aggsum. Previous code used 4 atomics to do aggsum_flush_bucket() and 2 more to re-borrow after the flush. But since asc_borrowed and asc_delta are accessed only while holding asc_lock, it makes no any sense to modify as_lower_bound and as_upper_bound in multiple steps. Instead of that the new code uses only 2 atomics in all the cases, one per as_*_bound variable. I think even that is overkill, simple atomic store and load could be used here, since all modifications are done under the as_lock, but there are no such primitives in ZFS code now. While there, make borrow code consider previous borrow value, so that on mixed request patterns reduce chance of needing to borrow again if much larger request follows tiny one that needed borrow. Also reduce as_numbuckets from uint64_t to u_int. It makes no sense to use so large division operation on every aggsum_add(). Reviewed by: Brian Behlendorf, Paul Dagnelie MFC after: 2 weeks Sponsored by: iXsystems, Inc. Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/aggsum.c head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/aggsum.h Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/aggsum.c ============================================================================== --- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/aggsum.c Thu Feb 6 20:18:45 2020 (r357638) +++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/aggsum.c Thu Feb 6 20:32:53 2020 (r357639) @@ -125,13 +125,11 @@ aggsum_flush_bucket(aggsum_t *as, struct aggsum_bucket * We use atomic instructions for this because we read the upper and * lower bounds without the lock, so we need stores to be atomic. */ - atomic_add_64((volatile uint64_t *)&as->as_lower_bound, asb->asc_delta); - atomic_add_64((volatile uint64_t *)&as->as_upper_bound, asb->asc_delta); - asb->asc_delta = 0; - atomic_add_64((volatile uint64_t *)&as->as_upper_bound, - -asb->asc_borrowed); atomic_add_64((volatile uint64_t *)&as->as_lower_bound, - asb->asc_borrowed); + asb->asc_delta + asb->asc_borrowed); + atomic_add_64((volatile uint64_t *)&as->as_upper_bound, + asb->asc_delta - asb->asc_borrowed); + asb->asc_delta = 0; asb->asc_borrowed = 0; } @@ -163,40 +161,43 @@ aggsum_value(aggsum_t *as) return (rv); } -static void -aggsum_borrow(aggsum_t *as, int64_t delta, struct aggsum_bucket *asb) -{ - int64_t abs_delta = (delta < 0 ? -delta : delta); - mutex_enter(&as->as_lock); - mutex_enter(&asb->asc_lock); - - aggsum_flush_bucket(as, asb); - - atomic_add_64((volatile uint64_t *)&as->as_upper_bound, abs_delta); - atomic_add_64((volatile uint64_t *)&as->as_lower_bound, -abs_delta); - asb->asc_borrowed = abs_delta; - - mutex_exit(&asb->asc_lock); - mutex_exit(&as->as_lock); -} - void aggsum_add(aggsum_t *as, int64_t delta) { struct aggsum_bucket *asb = &as->as_buckets[CPU_SEQID % as->as_numbuckets]; + int64_t borrow; - for (;;) { - mutex_enter(&asb->asc_lock); - if (asb->asc_delta + delta <= (int64_t)asb->asc_borrowed && - asb->asc_delta + delta >= -(int64_t)asb->asc_borrowed) { - asb->asc_delta += delta; - mutex_exit(&asb->asc_lock); - return; - } + /* Try fast path if we already borrowed enough before. */ + mutex_enter(&asb->asc_lock); + if (asb->asc_delta + delta <= (int64_t)asb->asc_borrowed && + asb->asc_delta + delta >= -(int64_t)asb->asc_borrowed) { + asb->asc_delta += delta; mutex_exit(&asb->asc_lock); - aggsum_borrow(as, delta * aggsum_borrow_multiplier, asb); + return; } + mutex_exit(&asb->asc_lock); + + /* + * We haven't borrowed enough. Take the global lock and borrow + * considering what is requested now and what we borrowed before. + */ + borrow = (delta < 0 ? -delta : delta) * aggsum_borrow_multiplier; + mutex_enter(&as->as_lock); + mutex_enter(&asb->asc_lock); + delta += asb->asc_delta; + asb->asc_delta = 0; + if (borrow >= asb->asc_borrowed) + borrow -= asb->asc_borrowed; + else + borrow = (borrow - (int64_t)asb->asc_borrowed) / 4; + asb->asc_borrowed += borrow; + atomic_add_64((volatile uint64_t *)&as->as_lower_bound, + delta - borrow); + atomic_add_64((volatile uint64_t *)&as->as_upper_bound, + delta + borrow); + mutex_exit(&asb->asc_lock); + mutex_exit(&as->as_lock); } /* Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/aggsum.h ============================================================================== --- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/aggsum.h Thu Feb 6 20:18:45 2020 (r357638) +++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/aggsum.h Thu Feb 6 20:32:53 2020 (r357639) @@ -39,7 +39,7 @@ typedef struct aggsum { kmutex_t as_lock; int64_t as_lower_bound; int64_t as_upper_bound; - uint64_t as_numbuckets; + uint_t as_numbuckets; aggsum_bucket_t *as_buckets; } aggsum_t;