On Wed, Aug 14, 2019 at 11:24 AM Julia Suvorova <jusual@xxxxxxxxxx> wrote:
>
> On Mon, Aug 12, 2019 at 6:03 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
> >
> > On 8/12/19 7:55 AM, Bart Van Assche wrote:
> > > On 8/12/19 5:39 AM, Julia Suvorova wrote:
> > >> -#define mb() asm volatile("mfence" ::: "memory")
> > >> -#define rmb() asm volatile("lfence" ::: "memory")
> > >> -#define wmb() asm volatile("sfence" ::: "memory")
> > >> -#define smp_rmb() barrier()
> > >> -#define smp_wmb() barrier()
> > >> +#define io_uring_mb() asm volatile("mfence" ::: "memory")
> > >> +#define io_uring_rmb() asm volatile("lfence" ::: "memory")
> > >> +#define io_uring_wmb() asm volatile("sfence" ::: "memory")
> > >> +#define io_uring_smp_rmb() io_uring_barrier()
> > >> +#define io_uring_smp_wmb() io_uring_barrier()
> > >
> > > Do users of liburing need these macros? If not, have you considered to
> > > move these macros to a new header file that is only used inside liburing
> > > and such that these macros are no longer visible to liburing users?
> >
> > The exposed API should not need any explicit barriers from the user,
> > so this suggestion makes a lot of sense to me.
>
> How about moving the definition of io_uring_cqe_seen() with whole
> io_uring_cq_advance() and io_uring_for_each_cqe() from liburing.h to
> queue.c? This way we can cover all barriers, and leave barrier.h local.
>
> Do you need io_uring_cq_advance and io_uring_for_each_cqe in the
> library?
>
This is one of the usage patterns:
io_uring_cqe* cqe;
int head;
int count = 0;
io_uring_for_each_cqe(&m_io_uring, head, cqe)
{
/* ... */
count++;
}
io_uring_cq_advance(&m_io_uring, count);
A little bit more performance is squeezed out this way.
Hrvoje Zeba
