From owner-svn-src-head@FreeBSD.ORG Wed Oct 24 20:29:23 2012 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id EBB8EC5; Wed, 24 Oct 2012 20:29:23 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-la0-f54.google.com (mail-la0-f54.google.com [209.85.215.54]) by mx1.freebsd.org (Postfix) with ESMTP id A43D28FC08; Wed, 24 Oct 2012 20:29:22 +0000 (UTC) Received: by mail-la0-f54.google.com with SMTP id e12so744739lag.13 for ; Wed, 24 Oct 2012 13:29:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:reply-to:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; bh=kmFK8M8YV5N4VgYQAeDl5+8XX5bCEM6QIgp/ggrWYbM=; b=cisCq7ulPePCjlkrIbFJWOPRrAGlv0QOF2roBO0hULkpzZCWFVfwnQyZ1eTdc+hNeD fzvNJj5Cu/sa+1/0ih00gq7TKveMmz4wA7kerrQZZxFuuZkHdiXHTEmLfT7gBCTHNYXV Q//G+J8xUckY6WcY8aPl2p09Tn+rtPS2Dm8tnmxp3D+Uvx9Msu/zRWD0H9WYWTP0jJ4p mP5L58z81krEYGvxzO9+UDhw+vS1ikiqsATV8htjxShfDe4lgiMFu0IlpK/e6Bq6u52G 0OMZXSEOwL+2v5DlRyz83iIDFUrs5gO2fpw+7KJf9ZaASV8jkPuGxwsGFZSjiv+WnUDr 1SgA== MIME-Version: 1.0 Received: by 10.112.41.36 with SMTP id c4mr6503122lbl.75.1351110561535; Wed, 24 Oct 2012 13:29:21 -0700 (PDT) Sender: asmrookie@gmail.com Received: by 10.112.30.37 with HTTP; Wed, 24 Oct 2012 13:29:21 -0700 (PDT) In-Reply-To: <50884E9F.3090706@freebsd.org> References: <201210241836.q9OIafqo073002@svn.freebsd.org> <201210241443.25988.jhb@freebsd.org> <50884E9F.3090706@freebsd.org> Date: Wed, 24 Oct 2012 21:29:21 +0100 X-Google-Sender-Auth: 1uW2pCK1ORDdDfMAZlH_Mwc9mis Message-ID: Subject: Re: svn commit: r242014 - head/sys/kern From: Attilio Rao To: Andre Oppermann Content-Type: text/plain; charset=UTF-8 Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Jim Harris , John Baldwin X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list Reply-To: attilio@FreeBSD.org List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 24 Oct 2012 20:29:24 -0000 On Wed, Oct 24, 2012 at 9:25 PM, Andre Oppermann wrote: > On 24.10.2012 21:06, Attilio Rao wrote: >> >> On Wed, Oct 24, 2012 at 8:00 PM, Jim Harris wrote: >>> >>> On Wed, Oct 24, 2012 at 11:43 AM, John Baldwin wrote: >>>> >>>> On Wednesday, October 24, 2012 2:36:41 pm Jim Harris wrote: >>>>> >>>>> Author: jimharris >>>>> Date: Wed Oct 24 18:36:41 2012 >>>>> New Revision: 242014 >>>>> URL: http://svn.freebsd.org/changeset/base/242014 >>>>> >>>>> Log: >>>>> Pad tdq_lock to avoid false sharing with tdq_load and tdq_cpu_idle. >>>>> >>>>> This enables CPU searches (which read tdq_load) to operate >>>>> independently >>>>> of any contention on the spinlock. Some scheduler-intensive >>>>> workloads >>>>> running on an 8C single-socket SNB Xeon show considerable >>>>> improvement with >>>>> this change (2-3% perf improvement, 5-6% decrease in CPU util). >>>>> >>>>> Sponsored by: Intel >>>>> Reviewed by: jeff >>>>> >>>>> Modified: >>>>> head/sys/kern/sched_ule.c >>>>> >>>>> Modified: head/sys/kern/sched_ule.c >>>>> >>>> >>>> ============================================================================== >>>>> >>>>> --- head/sys/kern/sched_ule.c Wed Oct 24 18:33:44 2012 (r242013) >>>>> +++ head/sys/kern/sched_ule.c Wed Oct 24 18:36:41 2012 (r242014) >>>>> @@ -223,8 +223,13 @@ static int sched_idlespinthresh = -1; >>>>> * locking in sched_pickcpu(); >>>>> */ >>>>> struct tdq { >>>>> - /* Ordered to improve efficiency of cpu_search() and switch(). */ >>>>> + /* >>>>> + * Ordered to improve efficiency of cpu_search() and switch(). >>>>> + * tdq_lock is padded to avoid false sharing with tdq_load and >>>>> + * tdq_cpu_idle. >>>>> + */ >>>>> struct mtx tdq_lock; /* run queue lock. */ >>>>> + char pad[64 - sizeof(struct mtx)]; >>>> >>>> >>>> Can this use 'tdq_lock __aligned(CACHE_LINE_SIZE)' instead? >>>> >>> >>> No - that doesn't pad it. I believe that only works if it's global, >>> i.e. not part of a data structure. >> >> >> As I've already said in another thread __align() doesn't work on >> object declaration, so what that won't pad it either if it is global >> or part of a struct. >> It is just implemented as __attribute__((aligned(X))): >> http://gcc.gnu.org/onlinedocs/gcc-3.2/gcc/Type-Attributes.html > > > Actually it seems gcc itself doesn't really care and it up to the > linker to honor that. Yes but the concept being that if you use __aligned() properly (when defining a struct) the object will be correctly sized, so you will get padding automatically. Attilio -- Peace can only be achieved by understanding - A. Einstein