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 572391D63F3; Wed, 26 Nov 2025 10:08:15 +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=1764151695; cv=none; b=XwtV9fiNo2EFVCFirm6+N1h0erq58UBCbWcyqdHC5mhDQcBy8uWfkcS0fXsVKNGYUfFBETT3bUMoWZ5LC3z4VzpYC4Ti1YxSE1XOZZsqH6h0MiMQ0cXS2v9LxFG8MRRTgNZZjfPSt4mf/qBbU6wDMyHVo1axZz27LibyBR2ms/Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764151695; c=relaxed/simple; bh=J2amtbAL4AoBVIXNA2h1zI+jiMqajl/5FLqHjIHMIFE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Ogtl6JZWTzUuQaV8EfKg03ITOuRxHh1i1Z76py7fWh4R1Jz6IQZxUgKGv4tf9Y8wHoPG1x2xmUKJNrhEinXLQs0jcAuZvK5q0WfFp8e6xs+yMmsp1urZSaSiIKFITHTO5X1M6VVoIhcj0DMNoVIKBQTpy3og+ab7MqDoDJoFhzY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bIwARS8H; 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="bIwARS8H" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8952AC113D0; Wed, 26 Nov 2025 10:08:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764151694; bh=J2amtbAL4AoBVIXNA2h1zI+jiMqajl/5FLqHjIHMIFE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bIwARS8H5bs26q/tiAHi3IcvLDbsKEIfDmQeQaRg//XqPZAOkyFTXZ7DBfAp888mn Az9zcHue7O2Syj9OGBUXKMe/7rDTc+3qTFQISBpdLAJ9uB+AU5sVUm6vqrkT0Hcz7F nZXafVhrdoJueR9+BbN1o3NFVofk/cj+uXVXf9fhTrX6bSRV+3cSOLZQor9AadE85D bmTGMDBw1VFSXP9+62gjSMdxUilUUczmhxWss1zaaXFWt3CHZzQ0smNw6CvaGCsk5F QNlecAnaNBBLYYysASJEaGxEWP5vKrjfgNuUcNN+ESTn8/rIxisC4ZLZvFQSobG0ry peXfGWV/QjKBA== Date: Wed, 26 Nov 2025 11:08:10 +0100 From: Christian Brauner To: Mateusz Guzik Cc: viro@zeniv.linux.org.uk, jack@suse.cz, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] fs: mark lookup_slow() as noinline Message-ID: <20251126-vermachen-sahne-c4f243016180@brauner> References: <20251119144930.2911698-1-mjguzik@gmail.com> <20251125-punkten-jegliche-5aee8187381d@brauner> 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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Nov 25, 2025 at 10:54:25AM +0100, Mateusz Guzik wrote: > On Tue, Nov 25, 2025 at 10:05 AM Christian Brauner wrote: > > > > On Wed, Nov 19, 2025 at 03:49:30PM +0100, Mateusz Guzik wrote: > > > Otherwise it gets inlined notably in walk_component(), which convinces > > > the compiler to push/pop additional registers in the fast path to > > > accomodate existence of the inlined version. > > > > > > Shortens the fast path of that routine from 87 to 71 bytes. > > > > > > Signed-off-by: Mateusz Guzik > > > --- > > > > Fwiw, the biggest problem is that we need to end up with something > > obvious so that we don't accidently destroy any potential performance > > gain in say 2 years because everyone forgot why we did things this way. > > > > I don't think there is a way around reviewing patches with an eye on > what they are doing to the fast path, on top of periodically checking > if whatever is considered the current compiler decided to start doing > something funky with it. > > I'm going to save a rant about benchmarking changes like these in the > current kernel for another day. Without knocking any tooling that we currently have but I don't think we have _meaningful_ performance testing - especially not automated.