From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C94BA1DFE16; Wed, 30 Oct 2024 08:22:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730276570; cv=none; b=cnZtMfaqlQ70GJfz+0rwe2uG5S4d+aYa8SahNuR/+2UtWjfv/jYEdbpfMCZNrqgy9TzMsrnZWots9XqWsqImDiq5AzLTxReols7Jak238y4i7sPi/myA95fUuF4Uo098MP10gSRuqldvzr0QtSmpplKsBe7xMjYk4E3DWUymeBM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730276570; c=relaxed/simple; bh=3M44dfapTogOZEkofhgJIny5tBNB1l5zW1bJlM7opcA=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=hf+y1MIDu4HsJ2e54rOaN8dFnVkr0AELrkjXj6JYZqfX02iBahdvRdNRrZvXZ0pXnP0OW90Bw2DtP5BEBHBuDPx5WBVAQBuSHq/3WAxW+RpkJI0gB1toyb0SgsOc4JtENDxjoqySGbahCD6PJNDehbRn4x4XsV5kqD6AxlikFZI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EajETXJv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EajETXJv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B242C4CEE4; Wed, 30 Oct 2024 08:22:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1730276570; bh=3M44dfapTogOZEkofhgJIny5tBNB1l5zW1bJlM7opcA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=EajETXJv8qf83oZumJdFmDKi1YuSTYcVJboRizdPM4kOF08PVYpgHsDuiL2irCxT/ BcSNBlc4YlEGpAEN/+4GoZlrBtwoH0KRLcyBjwsKvfuoaw/xsgo4owrb9KK8q+V/g6 Z45ExAUnwgBqaTjQmEWR2ZhdSAHI7RtsctQYQwGBjmUns1pDAhXykzfVRm8LWniZyI X626kEDouUsB/m4IuSDkecMChNtbfRLZgDM1vSvW47yIMO4cscfzTXic4mVZysjNXP 5e+zvgw2NDrdleYej6e4LakesMFMiEzkpUQhRvLmoQiGmmCM45+QhMVihPwfxm0t0d iXSaje5ZYKoFw== Received: from 82-132-233-180.dab.02.net ([82.132.233.180] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1t63yZ-008Bje-9r; Wed, 30 Oct 2024 08:22:47 +0000 Date: Wed, 30 Oct 2024 08:22:39 +0000 Message-ID: <87iktat2y8.wl-maz@kernel.org> From: Marc Zyngier To: Raghavendra Rao Ananta Cc: Oliver Upton , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org, syzbot Subject: Re: [PATCH v2] KVM: arm64: Get rid of userspace_irqchip_in_use In-Reply-To: References: <20241028234533.942542-1-rananta@google.com> <868qu63mdo.wl-maz@kernel.org> <865xpa3fwe.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/29.4 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-SA-Exim-Connect-IP: 82.132.233.180 X-SA-Exim-Rcpt-To: rananta@google.com, oliver.upton@linux.dev, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org, syzkaller@googlegroups.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Wed, 30 Oct 2024 00:16:48 +0000, Raghavendra Rao Ananta wrote: >=20 > On Tue, Oct 29, 2024 at 11:47=E2=80=AFAM Marc Zyngier wr= ote: > > > > On Tue, 29 Oct 2024 17:06:09 +0000, > > Raghavendra Rao Ananta wrote: > > > > > > On Tue, Oct 29, 2024 at 9:27=E2=80=AFAM Marc Zyngier = wrote: > > > > > > > > On Mon, 28 Oct 2024 23:45:33 +0000, > > > > Raghavendra Rao Ananta wrote: > > > > > > > > > Did you have a chance to check whether this had any negative impact= on > > > > actual workloads? Since the entry/exit code is a bit of a hot spot, > > > > I'd like to make sure we're not penalising the common case (I only > > > > wrote this patch while waiting in an airport, and didn't test it at > > > > all). > > > > > > > I ran the kvm selftests, kvm-unit-tests and booted a linux guest to > > > test the change and noticed no failures. > > > Any specific test you want to try out? > > > > My question is not about failures (I didn't expect any), but > > specifically about *performance*, and whether checking the flag > > without a static key can lead to any performance drop on the hot path. > > > > Can you please run an exit-heavy workload (such as hackbench, for > > example), and report any significant delta you could measure? >=20 > Oh, I see. I ran hackbench and micro-bench from kvm-unit-tests (which > also causes a lot of entry/exits), on Ampere Altra with kernel at > v6.12-rc1, and see no significant difference in perf. Thanks for running this stuff. > timer_10ms 231040.0 902= .0 > timer_10ms 234120.0 91= 4.0 This seems to be the only case were we are adversely affected by this change. In the grand scheme of thins, that's noise. But this gives us a clear line of sight for the removal of the in-kernel interrupts back to userspace. Thanks, M. --=20 Without deviation from the norm, progress is not possible.