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(pl@kamp.de@::ffff:172.20.250.13) by submission.kamp.de with ESMTPS (DHE-RSA-AES128-SHA encrypted) ESMTPA; 15 Jan 2021 15:39:18 -0000 Subject: Re: [PATCH 7/7] block/rbd: change request alignment to 1 byte To: dillaman@redhat.com References: <20201227164236.10143-1-pl@kamp.de> <20201227164236.10143-8-pl@kamp.de> From: Peter Lieven Message-ID: <75992ffb-3b6e-c31a-a9a0-956daa7752e6@kamp.de> Date: Fri, 15 Jan 2021 16:39:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=195.62.97.192; envelope-from=pl@kamp.de; helo=kerio.kamp.de X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Christian Theune , qemu-devel , qemu-block , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 15.01.21 um 16:27 schrieb Jason Dillaman: > On Thu, Jan 14, 2021 at 2:59 PM Peter Lieven wrote: >> Am 14.01.21 um 20:19 schrieb Jason Dillaman: >>> On Sun, Dec 27, 2020 at 11:42 AM Peter Lieven wrote: >>>> since we implement byte interfaces and librbd supports aio on byte granularity we can lift >>>> the 512 byte alignment. >>>> >>>> Signed-off-by: Peter Lieven >>>> --- >>>> block/rbd.c | 2 -- >>>> 1 file changed, 2 deletions(-) >>>> >>>> diff --git a/block/rbd.c b/block/rbd.c >>>> index 27b4404adf..8673e8f553 100644 >>>> --- a/block/rbd.c >>>> +++ b/block/rbd.c >>>> @@ -223,8 +223,6 @@ done: >>>> static void qemu_rbd_refresh_limits(BlockDriverState *bs, Error **errp) >>>> { >>>> BDRVRBDState *s = bs->opaque; >>>> - /* XXX Does RBD support AIO on less than 512-byte alignment? */ >>>> - bs->bl.request_alignment = 512; >>> Just a suggestion, but perhaps improve discard alignment, max discard, >>> optimal alignment (if that's something QEMU handles internally) if not >>> overridden by the user. >> >> Qemu supports max_discard and discard_alignment. Is there a call to get these limits >> >> from librbd? >> >> >> What do you mean by optimal_alignment? The object size? > krbd does a good job of initializing defaults [1] where optimal and > discard alignment is 64KiB (can actually be 4KiB now), max IO size for > writes, discards, and write-zeroes is the object size * the stripe > count. Okay, I will have a look at it. If qemu issues a write, discard, write_zero greater than obj_size  * stripe count will librbd split it internally or will the request fail? Regarding the alignment it seems that rbd_dev->opts->alloc_size is something that comes from the device configuration and not from rbd? I don't have that information inside the Qemu RBD driver. Peter