From owner-dev-commits-src-all@freebsd.org Fri Aug 20 21:18:22 2021 Return-Path: Delivered-To: dev-commits-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 9F3936671E2; Fri, 20 Aug 2021 21:18:22 +0000 (UTC) (envelope-from git@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) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4Grvct3t1Gz3Flh; Fri, 20 Aug 2021 21:18:22 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 6CFA02028F; Fri, 20 Aug 2021 21:18:22 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.16.1/8.16.1) with ESMTP id 17KLIMV4055749; Fri, 20 Aug 2021 21:18:22 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 17KLIMlx055748; Fri, 20 Aug 2021 21:18:22 GMT (envelope-from git) Date: Fri, 20 Aug 2021 21:18:22 GMT Message-Id: <202108202118.17KLIMlx055748@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Maxim Sobolev Subject: git: 0d13f5343faf - main - Only trigger read-ahead if two adjacent blocks have been requested. MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: sobomax X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: 0d13f5343fafbf3067ffc33a507ffca0375c4417 Auto-Submitted: auto-generated X-BeenThere: dev-commits-src-all@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Commit messages for all branches of the src repository List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 20 Aug 2021 21:18:22 -0000 The branch main has been updated by sobomax: URL: https://cgit.FreeBSD.org/src/commit/?id=0d13f5343fafbf3067ffc33a507ffca0375c4417 commit 0d13f5343fafbf3067ffc33a507ffca0375c4417 Author: Maxim Sobolev AuthorDate: 2021-08-20 19:33:51 +0000 Commit: Maxim Sobolev CommitDate: 2021-08-20 21:08:01 +0000 Only trigger read-ahead if two adjacent blocks have been requested. The change makes block caching algorithm to work better for remote media on low-BW/high-delay links. This cuts boot time over IP KVMs noticeably, since the initialization stage reads bunch of small 4th (and now lua) files that are not in the same cache stripe (usually), thus wasting lot of bandwidth and increasing latency even further. The original regression came in 2017 with revision 87ed2b7f5. We've seen increase of time it takes for the loader to get to the kernel loading from under a minute to 10-15 minutes in many cases. Reviewed by: tsoome MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D31623 --- stand/common/bcache.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/stand/common/bcache.c b/stand/common/bcache.c index a020f3c3c53c..526f9fe3fa5c 100644 --- a/stand/common/bcache.c +++ b/stand/common/bcache.c @@ -66,6 +66,7 @@ struct bcache { caddr_t bcache_data; size_t bcache_nblks; size_t ra; + daddr_t bcache_nextblkno; }; static u_int bcache_total_nblks; /* set by bcache_init */ @@ -163,6 +164,7 @@ bcache_allocate(void) } bcache_units++; bc->ra = BCACHE_READAHEAD; /* optimistic read ahead */ + bc->bcache_nextblkno = -1; return (bc); } @@ -291,6 +293,14 @@ read_strategy(void *devdata, int rw, daddr_t blk, size_t size, else ra = bc->bcache_nblks - BHASH(bc, p_blk + p_size); + /* + * Only trigger read-ahead if we detect two blocks being read + * sequentially. + */ + if ((bc->bcache_nextblkno != blk) && ra != 0) { + ra = 0; + } + if (ra != 0 && ra != bc->bcache_nblks) { /* do we have RA space? */ ra = MIN(bc->ra, ra - 1); ra = rounddown(ra, 16); /* multiple of 16 blocks */ @@ -342,8 +352,11 @@ read_strategy(void *devdata, int rw, daddr_t blk, size_t size, } done: - if ((result == 0) && (rsize != NULL)) - *rsize = size; + if (result == 0) { + if (rsize != NULL) + *rsize = size; + bc->bcache_nextblkno = blk + (size / DEV_BSIZE); + } return(result); }