Re: [blk] 8c5035dfbb: fio.read_iops -10.6% regression

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

Hi,

在 2022/10/09 16:43, Ming Lei 写道:
> On Sat, Oct 08, 2022 at 04:00:10PM +0800, Yu Kuai wrote:
> > Hi,
> >
> > 在 2022/10/08 10:50, kernel test robot 写道:
> > > Greeting,
> > >
> > > FYI, we noticed a -10.6% regression of fio.read_iops due to commit:
> >
> > I don't know how this is working but I'm *sure* this commit won't affect
>
> Looks it is wrong to move
>
> 	wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
>
> before rq_qos_add() in wbt_init().
>
> Without adding wbt rq_qos, wbt_set_write_cache is just a nop.

Yes, I got it now, I'm being foolish here.

I missed that "rwb->wc" is got by rq_qos in wbt_set_write_cache(), which
is NULL before rq_qos_add(). By the way, it's interesting that how read
performance is affected, I still don't know why yet...

Thanks,
Kuai
> thanks,
> Ming
>
> .