Am 15.01.21 um 16:27 schrieb Jason Dillaman:
> On Thu, Jan 14, 2021 at 2:59 PM Peter Lieven <p...@kamp.de> wrote:
>> Am 14.01.21 um 20:19 schrieb Jason Dillaman:
>>> On Sun, Dec 27, 2020 at 11:42 AM Peter Lieven <p...@kamp.de> 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 <p...@kamp.de>
>>>> ---
>>>> 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
