Re: Merging raw block device writes

[Jens Axboe <axboe@kernel.dk>]

On 11/26/23 11:59 PM, hch@lst.de wrote:
> On Sat, Nov 25, 2023 at 05:38:28PM +0000, Michael Kelley wrote:
>> Hyper-V guests and the Azure cloud have a particular interest here
>> because Hyper-V guests uses SCSI as the standard interface to virtual
>> disks.  Azure cloud disks can be throttled to a limited number of IOPS,
>> so the number of in-flights I/Os can be relatively high, and
>> merging can be beneficial to staying within the throttle
>> limits.  Of the flip side, this problem hasn't generated complaints
>> over the last 18 months that I'm aware of, though that may be more
>> because commercial distros haven't been running 5.16 or later kernels
>> until relatively recently.
> 
> I think the more important thing is that if you care about reducing
> the number of I/Os you probably should use an I/O scheduler.  Reducing
> the number of I/Os without an I/O scheduler isn't (and I'll argue
> shouldn't) be a concern for the non I/O scheduler.

Yep fully agree.

-- 
Jens Axboe