From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f45.google.com (mail-wr1-f45.google.com [209.85.221.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0157BDF61 for ; Tue, 2 Jan 2024 09:49:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="E5nzt+PV" Received: by mail-wr1-f45.google.com with SMTP id ffacd0b85a97d-33686649b72so9407982f8f.3 for ; Tue, 02 Jan 2024 01:49:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1704188975; x=1704793775; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:from:to:cc:subject:date:message-id :reply-to; bh=U9IdYDocnY8f+cYqz3KbusbOjRD+EWHCa+eZhkdi3Tg=; b=E5nzt+PVsC1WWw/GnNXeMOcIsWz9pMRLRdEWsVtHiIRalkCsM7gYCMI0fR1IDUnWq0 pH6tv44XRSYjs9XBan76wb6cG/RmQC59r8gD69XKAEu4GcqevuEwqSZxjDZmFza6Wle1 RZ9EwRkKPspdQ1XZnuvsX+d84BTsTVYyxbUNnR5vBAASdLNP9gi5vnV5Y0YaX0RrlGKE q170rjyHYQtm3ETmjeClzAEslYG7Hd/WURBteamKLR8aP8YYna9yZgQ9GaEfjvZ+nHlb 2h1ui4Ll4O/8PZqmtg1Zoq6jAzSmAiiOWyNxCV2wLDHJBJY7Wf5izKHrCvi5v+Ytr1yL aD1A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704188975; x=1704793775; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=U9IdYDocnY8f+cYqz3KbusbOjRD+EWHCa+eZhkdi3Tg=; b=ukhFREKROut5OKvUJo5akeJSc6oK/bXxCb29fOVJJJ7ATiV+2vwP3xqRGD7GtISqSu KRQm7CMjrIkeQd7cUCKg+icnjqZ0D8bak68g4dzzQaKJ8RDodQteMLQ/su9OVetVQ1Gc k9lDAZIs1feQ509Y8n0K7uAeXlJSxUjUnXhr51a6bqLjNzMQsDQ7CcbyfAkGc4l7oFaA HXVwl81qEEP5xW80rBO3RgnB3UKn+jGaoAf7AIPIearSnIS9zvH3OQO15odphohyIXmO wyKixSWkzpFbEShdpqLmIQvqwj7Wyw3+d1V6u7NXu+GuxvVxOLNDWV1R82cS+S3gfitA sL6Q== X-Gm-Message-State: AOJu0Yzy+zUey5atlI1uw96I+3M2eehA4AbnX1GvoHFykHQFw7VacPbN w0XTax2EBv8+d2PPV+1k8JM= X-Google-Smtp-Source: AGHT+IGFPcA3voqNTRf+D2XH2sdzWpXKt9lIQ2glivPEa9CMhBsId3NfbqvRNF+wplZBb2rOFINj4g== X-Received: by 2002:a5d:4bd0:0:b0:336:7790:6a36 with SMTP id l16-20020a5d4bd0000000b0033677906a36mr9470376wrt.129.1704188975145; Tue, 02 Jan 2024 01:49:35 -0800 (PST) Received: from gmail.com (195-38-113-95.pool.digikabel.hu. [195.38.113.95]) by smtp.gmail.com with ESMTPSA id h17-20020a5d4311000000b003373f723dcbsm5136543wrq.42.2024.01.02.01.49.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Jan 2024 01:49:34 -0800 (PST) Sender: Ingo Molnar Date: Tue, 2 Jan 2024 10:49:32 +0100 From: Ingo Molnar To: David Laight Cc: "'linux-kernel@vger.kernel.org'" , "'peterz@infradead.org'" , "'longman@redhat.com'" , "'mingo@redhat.com'" , "'will@kernel.org'" , "'boqun.feng@gmail.com'" , 'Linus Torvalds' , "'virtualization@lists.linux-foundation.org'" , 'Zeng Heng' Subject: Re: [PATCH next v2 2/5] locking/osq_lock: Optimise the vcpu_is_preempted() check. Message-ID: References: <2b4e8a5816a742d2bd23fdbaa8498e80@AcuMS.aculab.com> <3a9d1782cd50436c99ced8c10175bae6@AcuMS.aculab.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3a9d1782cd50436c99ced8c10175bae6@AcuMS.aculab.com> * David Laight wrote: > The vcpu_is_preempted() test stops osq_lock() spinning if a virtual > cpu is no longer running. > > Although patched out for bare-metal the code still needs the cpu number. Comma missing. > Reading this from 'prev->cpu' is a pretty much guaranteed have a cache miss > when osq_unlock() is waking up the next cpu. > > Instead save 'prev->cpu' in 'node->prev_cpu' and use that value instead. > Update in the osq_lock() 'unqueue' path when 'node->prev' is changed. > > This is simpler than checking for 'node->prev' changing and caching > 'prev->cpu'. Throughout the series, in changelogs and comments, please do: s/cpu /CPU Please be more careful about changelog quality. > struct optimistic_spin_node { > struct optimistic_spin_node *next, *prev; > - int locked; /* 1 if lock acquired */ > - int cpu; /* encoded CPU # + 1 value */ > + int locked; /* 1 if lock acquired */ > + int cpu; /* encoded CPU # + 1 value */ > + int prev_cpu; /* encoded CPU # + 1 value */ > }; s/ encoded CPU # + 1 value / encoded value: CPU+1 Thanks, Ingo