On Tue, Jan 23, 2024 at 12:13:29PM -0700, Jens Axboe wrote:
> On 1/23/24 11:36 AM, Bart Van Assche wrote:
> > On 1/23/24 09:34, Jens Axboe wrote:
> >> + struct {
> >> + spinlock_t lock;
> >> + spinlock_t zone_lock;
> >> + } ____cacheline_aligned_in_smp;
> >
> > It is not clear to me why the ____cacheline_aligned_in_smp attribute
> > is applied to the two spinlocks combined? Can this cause both spinlocks
> > to end up in the same cache line? If the ____cacheline_aligned_in_smp
> > attribute would be applied to each spinlock separately, could that
> > improve performance even further? Otherwise this patch looks good to me,
> > hence:
>
> It is somewhat counterintuitive, but my testing shows that there's no
> problem with them in the same cacheline. Hence I'm reluctant to move
> them out of the struct and align both of them, as it'd just waste memory
> for seemingly no runtime benefit.
Is there ay benefit in aligning either of them? The whole cache line
align locks thing seemed to have been very popular 20 years ago,
and these days it tends to not make much of a difference.
