From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 15F8C3858C31 for ; Thu, 23 Nov 2023 18:17:31 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 15F8C3858C31 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 15F8C3858C31 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1700763452; cv=none; b=u2oevkUpGID5laB0jzEV7+D1E5CUh605+sAsaIr7Q6Dpe0MYFL3dxsucpG0s1lXrMw/OcncqIV3SjJs43JXWi174GbKr/+NcvcIVwBY8CI7YaIRXSP5UFG5eERxiyF2mVR7pbiiTmm/iRtJVe0v+ykcgRQMq+CBujnEq2DiLKwU= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1700763452; c=relaxed/simple; bh=9zM6WDs/MZXFKccIgXOS50CjY9Nx86eeaLP6yrps9w8=; h=DKIM-Signature:From:To:Subject:Date:Message-ID:MIME-Version; b=drc53waIS1NmQICy6ymdIyw8c3m3agtVrrLyGIGfC+PylQVKv66yeb7puspFO9gj/k5YYXZrRWXOT48RyLoJ+i/iEQv6MZFA6ivVP/+KKQV6VOY0+kx3zFg2dLdmns1lpqr0lSd0Ds7AKfBTuHCjMjBQ/92TiCodTYm5ID50YDw= ARC-Authentication-Results: i=1; server2.sourceware.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1700763450; 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=6U995Zu/QGKUGldcqYFrCePJXjd/hGzBJtd119cBU9g=; b=fLSiA8KOHIaLMR+3sAVAvVUuA/k8NLFROiXiVWeEofbyqxXNeEqaRDojcHQeM9jaet12cc c+FWMnCKUu3x8GkO2rpBcikDq2TlTpZoqujrk40qAX8lI772HnSAcE/9bItjM8Z/QM+opM cG7NmKshdXer7ZUJZK6cJAk6creoS1w= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-434-5f2I9uo1Mxuv54Nsyq-3sg-1; Thu, 23 Nov 2023 13:17:27 -0500 X-MC-Unique: 5f2I9uo1Mxuv54Nsyq-3sg-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 52BCB101A529; Thu, 23 Nov 2023 18:17:27 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.108]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8697A492BE0; Thu, 23 Nov 2023 18:17:26 +0000 (UTC) From: Florian Weimer To: Wilco Dijkstra via Libc-alpha Cc: Wilco Dijkstra Subject: Re: [PATCH] Improve performance of libc locks References: Date: Thu, 23 Nov 2023 19:17:24 +0100 In-Reply-To: (Wilco Dijkstra via Libc-alpha's message of "Thu, 11 Aug 2022 16:22:56 +0000") Message-ID: <87h6lcbah7.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-9.6 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,LIKELY_SPAM_BODY,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: * Wilco Dijkstra via Libc-alpha: > Improve performance of libc locks by adding a fast path for the > single-threaded case. > > On Neoverse V1, a loop using rand() improved 3.6 times. Multithreaded > performance is unchanged. > > Passes regress on AArch64, OK for commit? > > --- > > diff --git a/sysdeps/nptl/libc-lockP.h b/sysdeps/nptl/libc-lockP.h > index d3a6837fd212f3f5dfd80f46d0e9ce365042ae0c..ccdb11fee6f14069d0b936be93d0f0fa6d8bc30b 100644 > --- a/sysdeps/nptl/libc-lockP.h > +++ b/sysdeps/nptl/libc-lockP.h > @@ -108,7 +108,14 @@ _Static_assert (LLL_LOCK_INITIALIZER == 0, "LLL_LOCK_INITIALIZER != 0"); > #define __libc_rwlock_fini(NAME) ((void) 0) > > /* Lock the named lock variable. */ > -#define __libc_lock_lock(NAME) ({ lll_lock (NAME, LLL_PRIVATE); 0; }) > +#define __libc_lock_lock(NAME) \ > + ({ \ > + if (SINGLE_THREAD_P) \ > + (NAME) = LLL_LOCK_INITIALIZER_LOCKED; \ > + else \ > + lll_lock (NAME, LLL_PRIVATE); \ > + 0; \ > + }) We already have SINGLE_THREAD_P checks around locking in several places. This makes the __libc_lock_lock check redudant in those cases. I believe this was done deliberately because in many cases, we can also to skip cancellation handling at the same time. The rand performance issue could be addressed with a similar localized change. I believe that would be far less controversial. Thanks, Florian