Re: [PATCH -next 2/3] md/raid10: convert resync_lock to use seqlock

[Yu Kuai]

Hi,

在 2022/09/02 17:42, Guoqing Jiang 写道:
> Hi,
>
> On 8/29/22 9:15 PM, Yu Kuai wrote:
> > +static bool wait_barrier_nolock(struct r10conf *conf)
> > +{
> > +    unsigned int seq = raw_read_seqcount(&conf->resync_lock.seqcount);
> > +
> > +    if (seq & 1)
> > +        return false;
> > +
> > +    if (READ_ONCE(conf->barrier))
> > +        return false;
> > +
> > +    atomic_inc(&conf->nr_pending);
> > +    if (!read_seqcount_retry(&conf->resync_lock.seqcount, seq))
>
> I think 'seq' is usually get from read_seqcount_begin.

read_seqcount_begin will loop untill "req & 1" failed, I'm afraid this
will cause high cpu usage in come cases.

What I try to do here is just try once, and fall back to hold lock and
wait if failed.

What do you think?

Thanks,
Kuai
> > +        return true;
> > +
> > +    atomic_dec(&conf->nr_pending);
> > +    return false;
> > +
>
> Thanks,
> Guoqing
> .