From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5D39ECD4F54 for ; Fri, 29 May 2026 13:40:26 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wSxRI-0006yD-7b; Fri, 29 May 2026 09:39:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wSxRD-0006xQ-Iz for qemu-devel@nongnu.org; Fri, 29 May 2026 09:39:48 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wSxRC-0004Uy-4Z for qemu-devel@nongnu.org; Fri, 29 May 2026 09:39:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1780061984; 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=wMt5rWqlm0F7EalJNfPMtguRYkVS3rsc7cHmyLCfcmE=; b=IXvMjnCL58ryFsuLRSgm9gMWSw/bg52bbHCpSmtHvzFv7HwuDkxeq1j9wOQjYSzhK7vW4j KGJUqlzRKCb2Iqrtj/TS+1W/FoKqzNECYGMriCGGduHmDAaeAvmDkJM7IMlnTQg0olNcuo 6mETXjt4oinbZFeshMob1qFliBpCLqA= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-685-aiqkoLPFP96JcNCe46KqQA-1; Fri, 29 May 2026 09:39:40 -0400 X-MC-Unique: aiqkoLPFP96JcNCe46KqQA-1 X-Mimecast-MFC-AGG-ID: aiqkoLPFP96JcNCe46KqQA_1780061979 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 078E2180034E; Fri, 29 May 2026 13:39:39 +0000 (UTC) Received: from redhat.com (unknown [10.44.33.95]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8234A180056E; Fri, 29 May 2026 13:39:37 +0000 (UTC) Date: Fri, 29 May 2026 15:39:34 +0200 From: Kevin Wolf To: Bin Guo Cc: qemu-devel@nongnu.org, stefanha@redhat.com Subject: Re: [PATCH] util/qemu-coroutine: skip global pool lock when pool is empty Message-ID: References: <20260529015423.49688-1-guobin@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260529015423.49688-1-guobin@linux.alibaba.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 29.05.2026 um 03:54 hat Bin Guo geschrieben: > coroutine_pool_refill_local() acquires global_pool_lock on every > call even when the global pool is empty (global_pool_size == 0). > Under high I/O concurrency many threads simultaneously attempt to > refill from an empty global pool, causing unnecessary mutex > contention. > > Add a fast-path check: read global_pool_size with qatomic_read() > before acquiring the mutex. If zero, the global pool is empty and > we return immediately. This is a racy read but correctness is > preserved: the only consequence of a stale read is a missed refill > opportunity, which will be retried on the next coroutine allocation. > > Signed-off-by: Bin Guo If you have any benchmark results, putting them in the commit message would be a good idea. (If you don't have them, you should probably get them for a patch that is motivated by performance.) Kevin