From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 289BA2B2DA for ; Mon, 13 Jan 2025 18:53:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736794413; cv=none; b=oGoegqq/wqzHhl6EQIavIuenR+BTgn6Vzp4jDC4WW+fHEAisElD/IBq3YJCb0bJDydkwsbMrm96GoC8Vz+MaXHYKI5QNN2zdjo6x8lHmQtvduAZZ3Y5JEKZfMr00q2u7497QDyDXRb4l6341ShE3THwknkZu875eFE920d9w72Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736794413; c=relaxed/simple; bh=2dkygM1+F7ng0CXJhY9rw5Uo2Gm1mS4UHZYlkhW+6JE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=fANa/oBY+wEGytPbCSh24eoQrZ+N1Cs10YIH+iBAVS0/PE508EsIYsTvNQ4FwWmZK7FN/B2mBsA/TDVn4o8nYCUV1b7oaWuH0h84WIEsLp+4l46BSrlKMsH+b7oDMbdn5E5Y+GnHe+44G97WFsJgECGsdtfSjfH26f6WSm2VFMs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=PBbJ+bCP; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="PBbJ+bCP" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1736794411; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=tN6TnFm2Xr2+2MnjTv8L6Mquqv9TtlwwwWgfBy/a+KM=; b=PBbJ+bCPrIkAYaol7WSC/p4O51mnxK7h0xPczsl5g6UfyyO3qaU4WdnOyhL6BW4F3bln5h TVkWSh3iJoOXS0iYgoyUbzBgSTO3dH1HZXfis8xrGQ9S4YfBm4MZAAA+PsDzjaF+V2Xd/s 44+7bAaDB9Er71Yad2pK2V5CWAm4rew= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-632-kmv7AmIpMjWz73eOauhPwA-1; Mon, 13 Jan 2025 13:53:27 -0500 X-MC-Unique: kmv7AmIpMjWz73eOauhPwA-1 X-Mimecast-MFC-AGG-ID: kmv7AmIpMjWz73eOauhPwA Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 40CB719560B7; Mon, 13 Jan 2025 18:53:26 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.5]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 753B6195608A; Mon, 13 Jan 2025 18:53:23 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 13 Jan 2025 19:53:01 +0100 (CET) Date: Mon, 13 Jan 2025 19:52:57 +0100 From: Oleg Nesterov To: kernel test robot Cc: oe-lkp@lists.linux.dev, lkp@intel.com, Christian Brauner , Christian Brauner , WangYuli , linux-fsdevel@vger.kernel.org Subject: Re: [brauner-vfs:vfs-6.14.misc] [pipe_read] aaec5a95d5: hackbench.throughput 7.5% regression Message-ID: <20250113185257.GA7471@redhat.com> References: <202501101015.90874b3a-lkp@intel.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202501101015.90874b3a-lkp@intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Well, I guess I need to react somehow... On 01/10, kernel test robot wrote: > > kernel test robot noticed a 7.5% regression of hackbench.throughput on: > > commit: aaec5a95d59615523db03dd53c2052f0a87beea7 ("pipe_read: don't wake up the writer if the pipe is still full") > https://git.kernel.org/cgit/linux/kernel/git/vfs/vfs.git vfs-6.14.misc Hmm. Not good ;) But otoh, > In addition to that, the commit also has significant impact on the following tests: > > +------------------+-------------------------------------------------------------------------------------------+ > | testcase: change | stress-ng: stress-ng.tee.ops_per_sec 500.7% improvement | So I hope we do not need to revert this patch? ------------------------------------------------------------------------------- I am looking at https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git/tree/src/hackbench/hackbench.c and I don't understand how can this patch make a noticable difference. And can't reproduce, hackbench -g 4 -f 10 --process --pipe -l 50000 -s 100 on my laptop under qemu doesn't show any regression. OK, in this case the early/unnecessary wakeup (removed by this patch) is not necessarily bad, when the woken writer actually gets CPU pipe_full() will be likely false, plus receiver() can wakeup more writers when it does the next read()s. But 7.5% ? Perhaps this is another case which shows that "artificial" benchmarks like this one are very sensitive... Or perhaps I am trying to deny the problem. So, Christian, et al, unless you think I should try to investigate, I am going to forget this report. If nothing else, "500.7% improvement" doesn't look bad even if I have no idea whether the stress-ng.tee.ops_per_sec test realistic or not (I have no idea what does it do). Oleg.