From owner-svn-src-all@freebsd.org Tue Feb 4 02:44:53 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 1742E239684; Tue, 4 Feb 2020 02:44:53 +0000 (UTC) (envelope-from jeff@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 48BTYw6vYHz4XP2; Tue, 4 Feb 2020 02:44:52 +0000 (UTC) (envelope-from jeff@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 C9578AC4B; Tue, 4 Feb 2020 02:44:52 +0000 (UTC) (envelope-from jeff@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 0142iq30037750; Tue, 4 Feb 2020 02:44:52 GMT (envelope-from jeff@FreeBSD.org) Received: (from jeff@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 0142iqXE037749; Tue, 4 Feb 2020 02:44:52 GMT (envelope-from jeff@FreeBSD.org) Message-Id: <202002040244.0142iqXE037749@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: jeff set sender to jeff@FreeBSD.org using -f From: Jeff Roberson Date: Tue, 4 Feb 2020 02:44:52 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r357487 - in head/sys: kern sys X-SVN-Group: head X-SVN-Commit-Author: jeff X-SVN-Commit-Paths: in head/sys: kern sys X-SVN-Commit-Revision: 357487 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: Tue, 04 Feb 2020 02:44:53 -0000 Author: jeff Date: Tue Feb 4 02:44:52 2020 New Revision: 357487 URL: https://svnweb.freebsd.org/changeset/base/357487 Log: Implement a deferred write advancement feature that can be used to further amortize shared cacheline writes. Discussed with: rlibby Differential Revision: https://reviews.freebsd.org/D23462 Modified: head/sys/kern/subr_smr.c head/sys/sys/smr.h Modified: head/sys/kern/subr_smr.c ============================================================================== --- head/sys/kern/subr_smr.c Tue Feb 4 02:42:54 2020 (r357486) +++ head/sys/kern/subr_smr.c Tue Feb 4 02:44:52 2020 (r357487) @@ -209,6 +209,26 @@ smr_advance(smr_t smr) return (goal); } +smr_seq_t +smr_advance_deferred(smr_t smr, int limit) +{ + smr_seq_t goal; + smr_t csmr; + + critical_enter(); + csmr = zpcpu_get(smr); + if (++csmr->c_deferred >= limit) { + goal = SMR_SEQ_INVALID; + csmr->c_deferred = 0; + } else + goal = smr_shared_current(csmr->c_shared) + SMR_SEQ_INCR; + critical_exit(); + if (goal != SMR_SEQ_INVALID) + return (goal); + + return (smr_advance(smr)); +} + /* * Poll to determine whether all readers have observed the 'goal' write * sequence number. @@ -255,6 +275,17 @@ smr_poll(smr_t smr, smr_seq_t goal, bool wait) * c_seq can only reference time after this wr_seq. */ s_wr_seq = atomic_load_acq_int(&s->s_wr_seq); + + /* + * This may have come from a deferred advance. Consider one + * increment past the current wr_seq valid and make sure we + * have advanced far enough to succeed. We simply add to avoid + * an additional fence. + */ + if (goal == s_wr_seq + SMR_SEQ_INCR) { + atomic_add_int(&s->s_wr_seq, SMR_SEQ_INCR); + s_wr_seq = goal; + } /* * Detect whether the goal is valid and has already been observed. Modified: head/sys/sys/smr.h ============================================================================== --- head/sys/sys/smr.h Tue Feb 4 02:42:54 2020 (r357486) +++ head/sys/sys/smr.h Tue Feb 4 02:44:52 2020 (r357487) @@ -64,6 +64,7 @@ typedef struct smr_shared *smr_shared_t; struct smr { smr_seq_t c_seq; /* Current observed sequence. */ smr_shared_t c_shared; /* Shared SMR state. */ + int c_deferred; /* Deferred advance counter. */ }; /* @@ -144,6 +145,13 @@ smr_exit(smr_t smr) * required to ensure that all modifications are visible to readers. */ smr_seq_t smr_advance(smr_t smr); + +/* + * Advances the write sequence number only after N calls. Returns + * the correct goal for a wr_seq that has not yet occurred. Used to + * minimize shared cacheline invalidations for frequent writers. + */ +smr_seq_t smr_advance_deferred(smr_t smr, int limit); /* * Returns true if a goal sequence has been reached. If