From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 C14C4192B95; Wed, 5 Feb 2025 16:00:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738771246; cv=none; b=DQRudB+DUX6nGPfjRmyh5AV4Yg7Nsocx59kWn4x7pF2NuguCA32WqEUs3E3jaGOIppnP0lTRC/2iQzgX2f19TajJOOq1d6K73um7TTiPgUH3TPmxPH8s99xpK9qzGFTN63O5AldYF0yaJTaEul5gdQ/RJg28bK91fyg6B1yTVAA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738771246; c=relaxed/simple; bh=+eZI6yISLtOCNguyEuiajeh+jRXwEj3Tqhyr4xhrF/0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Cv0ocfH5iBzLiRYes42DVedW6e08/atLT4mMA1ngeMQlOxn7IpMwxB3GHSly/3cEzg+4hol4f0CBai7iRRwMqJK40gCJeYlN/PSGaMA+SgaEcLC3lzY6M3GRqnt8RvQh2GqBwHiNCg4X9FShDIVdYWuGBO6JziGdnrDcoRTnag8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=G5IbGVuC; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="G5IbGVuC" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kHkOXmc0WL3fracXvIpybHt4FahneUTnJB7/Y+AClqo=; b=G5IbGVuCdXQeN9GGhWKEizwf5n jgZGhsG1JjkGjXUSvbGBHWtCPyIDDFPYqpcexFpYPBPiorZHz1Cng3YzJ9O+XGpQUjNngyFkNCynw UIBBBrB7xYuHKdkdOkLpGGLgdE4hjXWMyENPD1Y99HTdGOS/5CmwNA3n37VzbVJmatWH1tGCUHa0I 5t4fddwmIvZTkqmepGGp0ernbZK3EzyED2eT7oNUHfF4bJgIHnZ7c4Q/s5IEVuwU22CyQocUDUsKZ ZdSWk5Fth/pij80JV1cxjS5vQUQlvi+OckO2huG3KyLLOLHpuTdQgsOc7QE4R1mKayfknbs/WHUqZ 9rXImOjQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tfhpQ-00000003sxd-3RkR; Wed, 05 Feb 2025 16:00:40 +0000 Date: Wed, 5 Feb 2025 08:00:40 -0800 From: Christoph Hellwig To: "Martin K. Petersen" Cc: Christoph Hellwig , Mikulas Patocka , Jens Axboe , Alasdair Kergon , Mike Snitzer , Zdenek Kabelac , Milan Broz , linux-block@vger.kernel.org, dm-devel@lists.linux.dev Subject: Re: [PATCH] blk-settings: round down io_opt to at least 4K Message-ID: References: <81b399f6-55f5-4aa2-0f31-8b4f8a44e6a4@redhat.com> <28dcf41a-db7d-f8e7-d6b7-acef325c758c@redhat.com> Precedence: bulk X-Mailing-List: dm-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Tue, Feb 04, 2025 at 09:36:46PM -0500, Martin K. Petersen wrote: > > Christoph, > > >> Quite a few SCSI devices report 0xffff to indicate that the optimal > >> transfer length is the same as the maximum transfer length which for > >> low-byte commands is capped at 0xffff. That's where the odd value comes > >> from in some cases. > > > > Hmm, optimal == max is odd, > > What they mean to convey is that "device has no constraints". As opposed > to a value of 0 which means "not reported". I'm pretty sure that confuses some users, given normally optimal == lba size mean not reported. Either way we really need to document these somewhere.