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[2620:137:e000::1:20]) by mx.google.com with ESMTP id d26-20020a631d5a000000b00557888b4e8fsi7883313pgm.342.2023.06.27.13.52.32; Tue, 27 Jun 2023 13:52:45 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=Eo3jXY5o; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230324AbjF0UJg (ORCPT + 99 others); Tue, 27 Jun 2023 16:09:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229748AbjF0UJ2 (ORCPT ); Tue, 27 Jun 2023 16:09:28 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2CF226BD for ; Tue, 27 Jun 2023 13:08:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1687896521; 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; bh=rnusInJBPW2GEGronAXVDyjVA+cllAQmOUTk55olvn8=; b=Eo3jXY5ol5d0I84Hr6lLq/Rp+5RdXR6983YDVaYM+Wcx4ngNNK1e+6TxdUBjXiUVUSMgvs OzV5UW+LvPBaD5X7L2upcd0dRbbPScU8X9FOE9Mxa3cWvUPK6KD4l4xAw/UifeewRVO3eV 9ECMLjq4/uPpcQa+AdJEgGgwuL1WouI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-203-X3wHMvlBPX6bjTDWtTSNpw-1; Tue, 27 Jun 2023 16:08:37 -0400 X-MC-Unique: X3wHMvlBPX6bjTDWtTSNpw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E21B9104D51C; Tue, 27 Jun 2023 20:08:35 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6B775200BA86; Tue, 27 Jun 2023 20:08:35 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 30CBC400F7B5B; Tue, 27 Jun 2023 17:08:15 -0300 (-03) Date: Tue, 27 Jun 2023 17:08:15 -0300 From: Marcelo Tosatti To: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Cc: Alexander Viro , Christian Brauner , Matthew Wilcox , Christoph Hellwig , Jens Axboe , Frederic Weisbecker , Dave Chinner , Valentin Schneider , Leonardo Bras , Yair Podemsky , P J P Subject: [PATCH] fs/buffer.c: disable per-CPU buffer_head cache for isolated CPUs Message-ID: MIME-Version: 1.0 Content-Disposition: inline X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE, T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1769890555373967497?= X-GMAIL-MSGID: =?utf-8?q?1769890555373967497?= For certain types of applications (for example PLC software or RAN processing), upon occurrence of an event, it is necessary to complete a certain task in a maximum amount of time (deadline). One way to express this requirement is with a pair of numbers, deadline time and execution time, where: * deadline time: length of time between event and deadline. * execution time: length of time it takes for processing of event to occur on a particular hardware platform (uninterrupted). The particular values depend on use-case. For the case where the realtime application executes in a virtualized guest, an IPI which must be serviced in the host will cause the following sequence of events: 1) VM-exit 2) execution of IPI (and function call) 3) VM-entry Which causes an excess of 50us latency as observed by cyclictest (this violates the latency requirement of vRAN application with 1ms TTI, for example). invalidate_bh_lrus calls an IPI on each CPU that has non empty per-CPU cache: on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1); The performance when using the per-CPU LRU cache is as follows: 42 ns per __find_get_block 68 ns per __find_get_block_slow Given that the main use cases for latency sensitive applications do not involve block I/O (data necessary for program operation is locked in RAM), disable per-CPU buffer_head caches for isolated CPUs. Signed-off-by: Marcelo Tosatti Acked-by: Frederic Weisbecker diff --git a/fs/buffer.c b/fs/buffer.c index a7fc561758b1..49e9160ce100 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -49,6 +49,7 @@ #include #include #include +#include #include "internal.h" @@ -1289,7 +1290,7 @@ static void bh_lru_install(struct buffer_head *bh) * failing page migration. * Skip putting upcoming bh into bh_lru until migration is done. */ - if (lru_cache_disabled()) { + if (lru_cache_disabled() || cpu_is_isolated(smp_processor_id())) { bh_lru_unlock(); return; } @@ -1319,6 +1320,10 @@ lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size) check_irqs_on(); bh_lru_lock(); + if (cpu_is_isolated(smp_processor_id())) { + bh_lru_unlock(); + return NULL; + } for (i = 0; i < BH_LRU_SIZE; i++) { struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);