From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752533Ab2AZKD6 (ORCPT ); Thu, 26 Jan 2012 05:03:58 -0500 Received: from mail-ee0-f46.google.com ([74.125.83.46]:33004 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752305Ab2AZKDU (ORCPT ); Thu, 26 Jan 2012 05:03:20 -0500 From: Gilad Ben-Yossef To: linux-kernel@vger.kernel.org Cc: Gilad Ben-Yossef , Christoph Lameter , Chris Metcalf , Peter Zijlstra , Frederic Weisbecker , Russell King , linux-mm@kvack.org, Pekka Enberg , Matt Mackall , Sasha Levin , Rik van Riel , Andi Kleen , Mel Gorman , Andrew Morton , Alexander Viro , linux-fsdevel@vger.kernel.org, Avi Kivity , Michal Nazarewicz , Kosaki Motohiro , Milton Miller Subject: [v7 6/8] fs: only send IPI to invalidate LRU BH when needed Date: Thu, 26 Jan 2012 12:01:59 +0200 Message-Id: <1327572121-13673-7-git-send-email-gilad@benyossef.com> X-Mailer: git-send-email 1.7.0.4 In-Reply-To: <1327572121-13673-1-git-send-email-gilad@benyossef.com> References: <1327572121-13673-1-git-send-email-gilad@benyossef.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In several code paths, such as when unmounting a file system (but not only) we send an IPI to ask each cpu to invalidate its local LRU BHs. For multi-cores systems that have many cpus that may not have any LRU BH because they are idle or because they have not performed any file system accesses since last invalidation (e.g. CPU crunching on high perfomance computing nodes that write results to shared memory or only using filesystems that do not use the bh layer.) This can lead to loss of performance each time someone switches the KVM (the virtual keyboard and screen type, not the hypervisor) if it has a USB storage stuck in. This patch attempts to only send an IPI to cpus that have LRU BH. Signed-off-by: Gilad Ben-Yossef CC: Christoph Lameter CC: Chris Metcalf CC: Peter Zijlstra CC: Frederic Weisbecker CC: Russell King CC: linux-mm@kvack.org CC: Pekka Enberg CC: Matt Mackall CC: Sasha Levin CC: Rik van Riel CC: Andi Kleen CC: Mel Gorman CC: Andrew Morton CC: Alexander Viro CC: linux-fsdevel@vger.kernel.org CC: Avi Kivity CC: Michal Nazarewicz CC: Kosaki Motohiro CC: Milton Miller --- fs/buffer.c | 15 ++++++++++++++- 1 files changed, 14 insertions(+), 1 deletions(-) diff --git a/fs/buffer.c b/fs/buffer.c index 1a30db7..baa075e 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -1384,10 +1384,23 @@ static void invalidate_bh_lru(void *arg) } put_cpu_var(bh_lrus); } + +static bool has_bh_in_lru(int cpu, void *dummy) +{ + struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu); + int i; + for (i = 0; i < BH_LRU_SIZE; i++) { + if (b->bhs[i]) + return 1; + } + + return 0; +} + void invalidate_bh_lrus(void) { - on_each_cpu(invalidate_bh_lru, NULL, 1); + on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL); } EXPORT_SYMBOL_GPL(invalidate_bh_lrus); -- 1.7.0.4