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(pl@kamp.de@::ffff:172.20.250.32) by submission.kamp.de with ESMTPS (DHE-RSA-AES128-SHA encrypted) ESMTPA; 19 Jan 2021 09:36:28 -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> <75992ffb-3b6e-c31a-a9a0-956daa7752e6@kamp.de> From: Peter Lieven Message-ID: <1a83a103-33d5-6bfd-d6f8-87cf030521eb@kamp.de> Date: Tue, 19 Jan 2021 10:36:28 +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: 7bit 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.194, 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 18.01.21 um 23:33 schrieb Jason Dillaman: > On Fri, Jan 15, 2021 at 10:39 AM Peter Lieven wrote: >> 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? > librbd will handle it as needed. My goal is really just to get the > hints down the guest OS. > >> 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. > librbd doesn't really have the information either. The 64KiB guess > that krbd uses was a compromise since that was the default OSD > allocation size for HDDs since Luminous. Starting with Pacific that > default is going down to 4KiB. I will try to adjust these values as far as it is possible and makes sense. Is there a way to check the minimum supported OSD release in the backend from librbd / librados? Anyway, I want to sent a V2 by the end of this week. Peter