From owner-dev-commits-src-main@freebsd.org Mon Mar 8 23:54:31 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 5F6A355E12A; Mon, 8 Mar 2021 23:54:31 +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 4DvZvC2DzVz4T2Y; Mon, 8 Mar 2021 23:54:31 +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 3B4D011FEA; Mon, 8 Mar 2021 23:54:31 +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 128NsV3b044890; Mon, 8 Mar 2021 23:54:31 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 128NsVrA044889; Mon, 8 Mar 2021 23:54:31 GMT (envelope-from git) Date: Mon, 8 Mar 2021 23:54:31 GMT Message-Id: <202103082354.128NsVrA044889@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Alexander Motin Subject: git: 075e4807df3e - main - Do not read timer extra time when MWAIT is used. MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: mav X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: 075e4807df3e6b0d9196d56e4dbc33765d57e1f8 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: Mon, 08 Mar 2021 23:54:31 -0000 The branch main has been updated by mav: URL: https://cgit.FreeBSD.org/src/commit/?id=075e4807df3e6b0d9196d56e4dbc33765d57e1f8 commit 075e4807df3e6b0d9196d56e4dbc33765d57e1f8 Author: Alexander Motin AuthorDate: 2021-03-08 23:43:47 +0000 Commit: Alexander Motin CommitDate: 2021-03-08 23:43:47 +0000 Do not read timer extra time when MWAIT is used. When we enter C2+ state via memory read, it may take chipset some time to stop CPU. Extra register read covers that time. But MWAIT makes CPU stop immediately, so we don't need to waste time after wakeup with interrupts still disabled, increasing latency. On my system it reduces ping localhost latency, waking up all CPUs once a second, from 277us to 242us. MFC after: 1 month --- sys/dev/acpica/acpi_cpu.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/sys/dev/acpica/acpi_cpu.c b/sys/dev/acpica/acpi_cpu.c index 436dd9ddaa93..56182ed743de 100644 --- a/sys/dev/acpica/acpi_cpu.c +++ b/sys/dev/acpica/acpi_cpu.c @@ -1220,18 +1220,19 @@ acpi_cpu_idle(sbintime_t sbt) start_time = 0; cputicks = cpu_ticks(); } - if (cx_next->do_mwait) + if (cx_next->do_mwait) { acpi_cpu_idle_mwait(cx_next->mwait_hint); - else + } else { CPU_GET_REG(cx_next->p_lvlx, 1); + /* + * Read the end time twice. Since it may take an arbitrary time + * to enter the idle state, the first read may be executed before + * the processor has stopped. Doing it again provides enough + * margin that we are certain to have a correct value. + */ + AcpiGetTimer(&end_time); + } - /* - * Read the end time twice. Since it may take an arbitrary time - * to enter the idle state, the first read may be executed before - * the processor has stopped. Doing it again provides enough - * margin that we are certain to have a correct value. - */ - AcpiGetTimer(&end_time); if (cx_next->type == ACPI_STATE_C3) { AcpiGetTimer(&end_time); AcpiGetTimerDuration(start_time, end_time, &end_time);