From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D3E0C433EF for ; Thu, 28 Oct 2021 20:33:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 61FD660F0F for ; Thu, 28 Oct 2021 20:33:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231201AbhJ1Ufp (ORCPT ); Thu, 28 Oct 2021 16:35:45 -0400 Received: from bedivere.hansenpartnership.com ([96.44.175.130]:51762 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230323AbhJ1Ufp (ORCPT ); Thu, 28 Oct 2021 16:35:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=hansenpartnership.com; s=20151216; t=1635453198; bh=cSZBm0trHz1EnFTZoBXBXvs8X4Y8AfvRTslBGZ+VMEU=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References:From; b=T7A0/ovwPsaP1m0wEvOR2VhCtiZMK9rRu+OM/OaqVp11IBHMkHXp0pd8+AtIxsPdF L1L4NtVxekNGT/TF3F2ryXi+WYhuW8X2lsyFShDk0BPnB2U/BfrfoKIGpcM9kfInDS fy30iPfEdFd/3B30/j7gN4tAWcJTYKp7s5DPkrZw= Received: from localhost (localhost [127.0.0.1]) by bedivere.hansenpartnership.com (Postfix) with ESMTP id 12FD21280CAB; Thu, 28 Oct 2021 16:33:18 -0400 (EDT) Received: from bedivere.hansenpartnership.com ([127.0.0.1]) by localhost (bedivere.hansenpartnership.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ETgKuIeG6ep6; Thu, 28 Oct 2021 16:33:18 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=hansenpartnership.com; s=20151216; t=1635453197; bh=cSZBm0trHz1EnFTZoBXBXvs8X4Y8AfvRTslBGZ+VMEU=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References:From; b=RQ2V1m0kPrFTWeAUpbc7TfIpKCj17D/qdRGUrl052MNYP8DPpk89EnjTMbHhK63Yd 2tGuMY94LlZXWm3VQWbFOHDpV7QzD7NkN8VxX4yKfvR/SjFC6PnG54SccGtiuH/JL+ XLQnjMsqzSIGwg5NWCjzwzzZxl9c/vTvkhoN2dHM= Received: from jarvis.int.hansenpartnership.com (unknown [IPv6:2601:5c4:4300:c551::527]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by bedivere.hansenpartnership.com (Postfix) with ESMTPSA id 178EA1280CA9; Thu, 28 Oct 2021 16:33:17 -0400 (EDT) Message-ID: <4f16a99974be6f2a0f207d5ca7327719cdf4e36e.camel@HansenPartnership.com> Subject: Re: [PATCH] scsi: ufs: mark HPB support as BROKEN From: James Bottomley To: Bart Van Assche , Christoph Hellwig Cc: "Martin K. Petersen" , Jens Axboe , Jaegeuk Kim , alim.akhtar@samsung.com, avri.altman@wdc.com, linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, Daejun Park Date: Thu, 28 Oct 2021 16:33:15 -0400 In-Reply-To: References: <20211026071204.1709318-1-hch@lst.de> <99641481-523a-e5a9-db48-dac2b547b4bd@acm.org> <7ed11ee1f8beca9a27c0cb2eb0dcea4dbd557961.camel@HansenPartnership.com> <870e986c-08dd-2fa2-a593-0f97e10d6df5@kernel.dk> <4438ab72-7da0-33de-ecc9-91c3c179eca7@acm.org> <36729509daa80fd48453e8a3a1b5c23750948e6c.camel@HansenPartnership.com> <679b4d3b-778e-47cd-d53f-f7bf77315f7c@acm.org> <20211027052724.GA8946@lst.de> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.34.4 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, 2021-10-28 at 13:21 -0700, Bart Van Assche wrote: [...] > Hi James, > > The help with trying to find a solution is appreciated. > > One of the software developers who is familiar with HPB explained to > me that READ BUFFER and WRITE BUFFER commands may be received in an > arbitrary order by UFS devices. The UFS HPB spec requires UFS devices > to be able to stash up to 128 such pairs. I'm concerned that leaving > out WRITE BUFFER commands only will break the HPB protocol in a > subtle way. Based on the publicly available information (the hotstorage paper) I don't belive it can. The Samsung guys also appear to confirm that the use of WRITE BUFFER is simply an optimzation for large requests: https://lore.kernel.org/all/20211025051654epcms2p36b259d237eb2b8b885210148118c5d3f@epcms2p3/ As did the excerpt from the spec you posted. It will cause slowdowns for reads of > 32kb, because they have to go through the native FTL lookup now, but there shouldn't be any functional change. Unless there's anything else in the proprietary spec that contradicts this? James