On 5/29/22 12:07 PM, Hao Xu wrote:
> On 5/30/22 00:25, Jens Axboe wrote:
>> On 5/29/22 10:20 AM, Hao Xu wrote:
>>> From: Hao Xu <howeyxu@xxxxxxxxxxx>
>>>
>>> From: Hao Xu <howeyxu@xxxxxxxxxxx>
>>>
>>> Use per list lock for cancel_hash, this removes some completion lock
>>> invocation and remove contension between different cancel_hash entries
>>
>> Interesting, do you have any numbers on this?
>
> Just Theoretically for now, I'll do some tests tomorrow. This is
> actually RFC, forgot to change the subject.
>
>>
>> Also, I'd make a hash bucket struct:
>>
>> struct io_hash_bucket {
>> spinlock_t lock;
>> struct hlist_head list;
>> };
>>
>> rather than two separate structs, that'll have nicer memory locality too
>> and should further improve it. Could be done as a prep patch with the
>> old locking in place, making the end patch doing the per-bucket lock
>> simpler as well.
>
> Sure, if the test number make sense, I'll send v2. I'll test the
> hlist_bl list as well(the comment of it says it is much slower than
> normal spin_lock, but we may not care the efficiency of poll
> cancellation very much?).
I don't think the bit spinlocks are going to be useful, we should
stick with a spinlock for this. They are indeed slower and generally not
used for that reason. For a use case where you need a ton of locks and
saving the 4 bytes for a spinlock would make sense (or maybe not
changing some struct?), maybe they have a purpose. But not for this.
--
Jens Axboe
