From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9CEE01F26C0 for ; Fri, 8 Nov 2024 20:07:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731096481; cv=none; b=MUpzGlwA620JowOXxdbPXOkSqy6hIVuMS8DwHxqkxOvPMqkC4jvY8QLkDdJOcbyil7QOjObgqzldg7XI6K5UlSPtnnb8CLcgyjWDSkxQjoyzk9sRG32qe1exSmB6HbghXd2TBif10FySynveSz2eghBuhsBBRC6A6Q58LBotvWI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731096481; c=relaxed/simple; bh=1K1pLssV5ZrYFU3AqLaKLNrDoQpz99T6UPphEacdFUo=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=SrJXw5vBzIMj/uuShFfKvKqLrAyO0k5RatinjOhbBUrwvXlNbXtpwDM49o1fUAmZi5zSWUxrpAWFC0ZQZCQsmBthEUB+docSFRfFe+bJi+DnMAtR3Ex3WVfi9Owy4r6y/rx0F0SucCEPr4dMk9TRGM3pFe/tTcNmzpT3X7JNXbA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=shelob.surriel.com; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=shelob.surriel.com Received: from [2601:18c:9101:a8b6:6e0b:84ff:fee2:98bb] (helo=imladris.surriel.com) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1t9VGO-000000002Kg-0K1C; Fri, 08 Nov 2024 15:07:24 -0500 Message-ID: <55ada30f76d544a3f700e57a01cb6f6f255581d5.camel@surriel.com> Subject: Re: [PATCH] x86,tlb: update mm_cpumask lazily From: Rik van Riel To: Dave Hansen , Dave Hansen Cc: Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, kernel-team@meta.com Date: Fri, 08 Nov 2024 15:07:23 -0500 In-Reply-To: <4f7d5752-41eb-4828-8bd8-9bd07e89f4f0@intel.com> References: <20241108143144.2f15fe35@imladris.surriel.com> <4f7d5752-41eb-4828-8bd8-9bd07e89f4f0@intel.com> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Sender: riel@surriel.com On Fri, 2024-11-08 at 12:03 -0800, Dave Hansen wrote: > On 11/8/24 11:31, Rik van Riel wrote: > > =C2=A0 /* Start receiving IPIs and then read tlb_gen (and > > LAM below) */ > > - if (next !=3D &init_mm) > > + if (next !=3D &init_mm && !cpumask_test_cpu(cpu, > > mm_cpumask(next))) > > =C2=A0 cpumask_set_cpu(cpu, mm_cpumask(next)); > > =C2=A0 next_tlb_gen =3D atomic64_read(&next- > > >context.tlb_gen); >=20 > If we're worried about contention on mm_cpumask(), then this hunk > makes > sense independently of the lazy updating. We might want to take this > hunk forward before we do the rest because this seems like a no- > brainer. >=20 If we always clear the CPU in the mm_cpumask when prev !=3D next, wouldn't that result in that CPU's bit being clear (and needing to be set) for next when prev !=3D next? What am I missing? --=20 All Rights Reversed.