From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 B975E20E6F0 for ; Thu, 23 Jan 2025 12:56:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737637007; cv=none; b=g2IzSCNmex1hfwcmconiLrVgsqMoKzlGA1bBUyLmNHDPB0SSQU1l2YJg0uSHJaVHHyQ63Q7oZZpUI4ls+2oHJaVA+ZcMO164WqyDp3pSuaqiHL+2xBb43jGJfHXD7bPZbK806u9902QbYQPV4A5+QCZAOl/dacOP1Fo3RlpO/bA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737637007; c=relaxed/simple; bh=uNA4qMy5D/nSQ/qCnJsdSnhHTssNBm2lRMEc44lDcNI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ZLK2srT2gMU5TZEo1k9jusQpOejSMprtrvZkbQrUfVOl/yI8/xjdFJhanzOhSmgEBK1//23KBV0GiJrzMXph4u7ptspAqHfo5bQ8X2MXIIKPilExbbp4xfoqBst85VxbnVzMCpDwSNPzMHRLUJk/ZzRW/lHwKPbrdgdjBVry4fs= 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=cCRjEH7m; arc=none smtp.client-ip=170.10.129.124 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="cCRjEH7m" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1737637004; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=uNA4qMy5D/nSQ/qCnJsdSnhHTssNBm2lRMEc44lDcNI=; b=cCRjEH7mgOuP9CI7g+/DyU3yYTEaLDPo0s/pZVGoaE9MYN7a5Xcf8OLnP4XjJv7JTSbTRo lhtu+wx9WOjf82CasaYIhdAm/IAp/HacIrX0XpRQ3gwTpLdA7eeQHtQ1JbtXW+A5YdQr4F 6hsYi4Sw39V8LbmT+mo5Qlp1YPBqDok= Received: from mx-prod-mc-02.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-561-RiA7HC03OAuSWWDVQ0D7Cw-1; Thu, 23 Jan 2025 07:56:40 -0500 X-MC-Unique: RiA7HC03OAuSWWDVQ0D7Cw-1 X-Mimecast-MFC-AGG-ID: RiA7HC03OAuSWWDVQ0D7Cw 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-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E67181955DE0; Thu, 23 Jan 2025 12:56:37 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.226.64]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 0C658195608A; Thu, 23 Jan 2025 12:56:34 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 23 Jan 2025 13:56:11 +0100 (CET) Date: Thu, 23 Jan 2025 13:56:08 +0100 From: Oleg Nesterov To: Mateusz Guzik Cc: kernel test robot , oe-lkp@lists.linux.dev, lkp@intel.com, Christian Brauner , WangYuli , linux-fsdevel@vger.kernel.org Subject: Re: [linux-next:master] [pipe_read] aaec5a95d5: stress-ng.poll.ops_per_sec 11.1% regression Message-ID: <20250123125607.GA16498@redhat.com> References: <202501201311.6d25a0b9-lkp@intel.com> <20250120121928.GA7432@redhat.com> <20250120124209.GB7432@redhat.com> <20250120203118.GF7432@redhat.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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Sorry for delay, On 01/20, Mateusz Guzik wrote: > > On Mon, Jan 20, 2025 at 9:31 PM Oleg Nesterov wrote: > > I'm afraid my emails can look as if I am trying to deny the problem. > > No. Just I think we need to understand why exactly this patch makes > > a difference. > > > > I agree. > > I was going to state there is 0 urgency as long as the patch does not > make the merge window, but it just did. Yes... > So one would preferably survey a bunch of real workloads, see what > happens with real pipes with both policies -- the early wake up is > basically a tradeoff and it very well may be it is worth it in the > real world. The problem is that this early wakeup is not intended, the code is not supposed to do this. So in some sense this patch fixes the intended/documented "avoid unnecessary wakeups" logic. Now I can reproduce the hackbench's slowdown on my laptop, but still don't understand it... I'll try to think more on Weekend, then I'll discuss the possible revert with Linus who wrote that code and reviewed this patch. Thanks for your investigations, Oleg.