Re: [PATCH v5 1/2] io_uring: minor io_cqring_wait() optimization

Re: [PATCH v5 1/2] io_uring: minor io_cqring_wait() optimization

[Jens Axboe]

On 3/8/22 10:36 PM, Olivier Langlois wrote:
> On Tue, 2022-03-08 at 17:54 -0700, Jens Axboe wrote:
>> On 3/8/22 3:17 PM, Olivier Langlois wrote:
>>> Move up the block manipulating the sig variable to execute code
>>> that may encounter an error and exit first before continuing
>>> executing the rest of the function and avoid useless computations
>>
>> I don't think this is worthwhile doing. If you're hitting an error
>> in any of them, it's by definition not the fast path.
>>
> Well, by itself it is not a big improvement but it is still an
> improvement.
> 
> but most importantly, it has to be considered in the context of the
> current patchset because in patch #2, the following step is to
> 
> 1. acquire the napi spin lock
> 2. splice the context napi list into a local one.
> 3. release the lock
> 
> If this patch is not in place before patch #2, you would need undo all
> that before returning from the sig block which would make the function
> bigger when all that is completely avoidable by accepting this patch...
> 
> Both patches were together in v1 but I decided to break them apart
> thinking that this was the right thing to do...

Yeah ok, it does make sense in the context of patch 2. Thanks!

-- 
Jens Axboe

Re: [PATCH v5 0/2] io_uring: Add support for napi_busy_poll

[Jens Axboe]

On 3/8/22 10:47 PM, Olivier Langlois wrote:
> On Tue, 2022-03-08 at 17:54 -0700, Jens Axboe wrote:
>> On 3/8/22 3:17 PM, Olivier Langlois wrote:
>>> The sqpoll thread can be used for performing the napi busy poll in
>>> a
>>> similar way that it does io polling for file systems supporting
>>> direct
>>> access bypassing the page cache.
>>>
>>> The other way that io_uring can be used for napi busy poll is by
>>> calling io_uring_enter() to get events.
>>>
>>> If the user specify a timeout value, it is distributed between
>>> polling
>>> and sleeping by using the systemwide setting
>>> /proc/sys/net/core/busy_poll.
>>
>> I think we should get this queued up, but it doesn't apply to
>> for-5.18/io_uring at all. I can fix it up, but just curious what you
>> tested against?
>>
> Hi Jens,
> 
> I did wrote the patch from
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> 
> My testing systems are based on 5.16. I have backported the patch and
> compiled 5.16.12 with the patch for my testing.
> 
> sorry if I didn't use the right repo...

Generally, since the patch is for 5.18, you'd want to base it on my
for-5.18/io_uring branch as then it would apply on top of what is
already pending. But I'll see if I can shoe horn it, unfortunately we'll
hit a merge error but it'll be minor.

-- 
Jens Axboe