From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f177.google.com (mail-we0-f177.google.com [74.125.82.177]) by kanga.kvack.org (Postfix) with ESMTP id 5C8166B0036 for ; Mon, 16 Dec 2013 08:44:55 -0500 (EST) Received: by mail-we0-f177.google.com with SMTP id u56so4484044wes.8 for ; Mon, 16 Dec 2013 05:44:54 -0800 (PST) Received: from mail-ea0-x22b.google.com (mail-ea0-x22b.google.com [2a00:1450:4013:c01::22b]) by mx.google.com with ESMTPS id wj1si5054545wjb.46.2013.12.16.05.44.54 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 16 Dec 2013 05:44:54 -0800 (PST) Received: by mail-ea0-f171.google.com with SMTP id h10so2234245eak.2 for ; Mon, 16 Dec 2013 05:44:54 -0800 (PST) Date: Mon, 16 Dec 2013 14:44:49 +0100 From: Ingo Molnar Subject: Re: [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB range flush v2 Message-ID: <20131216134449.GA3034@gmail.com> References: <1386964870-6690-1-git-send-email-mgorman@suse.de> <20131215155539.GM11295@suse.de> <20131216102439.GA21624@gmail.com> <20131216125923.GS11295@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131216125923.GS11295@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Linus Torvalds , Alex Shi , Thomas Gleixner , Andrew Morton , Fengguang Wu , H Peter Anvin , Linux-X86 , Linux-MM , LKML , Peter Zijlstra * Mel Gorman wrote: > > Whatever we did right in v3.4 we want to do in v3.13 as well - or > > at least understand it. > > Also agreed. I started a bisection before answering this mail. It > would be cooler and potentially faster to figure it out from direct > analysis but bisection is reliable and less guesswork. Trying to guess can potentially last a _lot_ longer than a generic, no-assumptions bisection ... The symptoms could point to anything: scheduler, locking details, some stupid little change in a wakeup sequence somewhere, etc. It might even be a non-deterministic effect of some timing change causing the workload 'just' to avoid a common point of preemption and not scheduling as much - and become more unfair and thus certain threads lasting longer to finish. Does the benchmark execute a fixed amount of transactions per thread? That might artificially increase the numeric regression: with more threads it 'magnifies' any unfairness effects because slower threads will become slower, faster threads will become faster, as the thread count increases. [ That in itself is somewhat artificial, because real workloads tend to balance between threads dynamically and don't insist on keeping the fastest threads idle near the end of a run. It does not invalidate the complaint about the unfairness itself, obviously. ] Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org