From owner-dev-commits-src-main@freebsd.org Sun Oct 3 21:57:00 2021 Return-Path: Delivered-To: dev-commits-src-main@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 06D5666FEA7; Sun, 3 Oct 2021 21:57:00 +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 4HMyP76Gs5z4gRg; Sun, 3 Oct 2021 21:56:59 +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 B36AE5966; Sun, 3 Oct 2021 21:56:59 +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 193Lux54041353; Sun, 3 Oct 2021 21:56:59 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 193Luxix041352; Sun, 3 Oct 2021 21:56:59 GMT (envelope-from git) Date: Sun, 3 Oct 2021 21:56:59 GMT Message-Id: <202110032156.193Luxix041352@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Colin Percival Subject: git: b841148bbbdc - main - loader: Refactor readahead adjustment in bcache MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: cperciva X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: b841148bbbdc967c871e8742a6f0b7b17b2d1d91 Auto-Submitted: auto-generated X-BeenThere: dev-commits-src-main@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Commit messages for the main branch of the src repository List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 03 Oct 2021 21:57:00 -0000 The branch main has been updated by cperciva: URL: https://cgit.FreeBSD.org/src/commit/?id=b841148bbbdc967c871e8742a6f0b7b17b2d1d91 commit b841148bbbdc967c871e8742a6f0b7b17b2d1d91 Author: Colin Percival AuthorDate: 2021-10-03 19:10:36 +0000 Commit: Colin Percival CommitDate: 2021-10-03 19:10:36 +0000 loader: Refactor readahead adjustment in bcache While I'm here, add an explanatory comment. No functional change intended. Reviewed by: imp, tsoome (previous version) MFC after: 1 week Sponsored by: https://patreon.com/cperciva Differential Revision: https://reviews.freebsd.org/D32249 --- stand/common/bcache.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/stand/common/bcache.c b/stand/common/bcache.c index 0eeb7e74ee96..b3b8b22c7d21 100644 --- a/stand/common/bcache.c +++ b/stand/common/bcache.c @@ -238,17 +238,27 @@ read_strategy(void *devdata, int rw, daddr_t blk, size_t size, if (BCACHE_LOOKUP(bc, (daddr_t)(blk + i))) { bcache_misses += (nblk - i); complete = 0; - if (nblk - i > BCACHE_MINREADAHEAD && bc->ra > BCACHE_MINREADAHEAD) - bc->ra >>= 1; /* reduce read ahead */ break; } else { bcache_hits++; } } - if (complete) { /* whole set was in cache, return it */ + /* + * Adjust read-ahead size if appropriate. Subject to the requirement + * that bc->ra must stay in between MINREADAHEAD and READAHEAD, we + * increase it when we notice that readahead was useful and decrease + * it when we notice that readahead was not useful. + */ + if (complete) { if (bc->ra < BCACHE_READAHEAD) - bc->ra <<= 1; /* increase read ahead */ + bc->ra <<= 1; /* increase read ahead */ + } else { + if (nblk - i > BCACHE_MINREADAHEAD && bc->ra > BCACHE_MINREADAHEAD) + bc->ra >>= 1; /* reduce read ahead */ + } + + if (complete) { /* whole set was in cache, return it */ bcopy(bc->bcache_data + (bcache_blksize * BHASH(bc, blk)), buf, size); goto done; }