[LTP] [PATCH v2] read_all: retry to queue work for any worker

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> Hi Jan,
> 
> On Fri, Oct 11, 2019 at 4:24 PM Li Wang <liwang@redhat.com> wrote:
> 
> >
> >
> > On Wed, Oct 9, 2019 at 10:43 PM Jan Stancek <jstancek@redhat.com> wrote:
> >
> >> read_all is currently retrying only for short time period and it's
> >> retrying to queue for same worker. If that worker is busy, it easily
> >> hits timeout.
> >>
> >> For example 'kernel_page_tables' on aarch64 can take long time to
> >> open/read:
> >>   # time dd if=/sys/kernel/debug/kernel_page_tables of=/dev/null count=1
> >> bs=1024
> >>   1+0 records in
> >>   1+0 records out
> >>   1024 bytes (1.0 kB, 1.0 KiB) copied, 13.0531 s, 0.1 kB/s
> >>
> >>   real    0m13.066s
> >>   user    0m0.000s
> >>   sys     0m13.059s
> >>
> >> Rather than retrying to queue for specific worker, pick any that can
> >> accept
> >> the work and keep trying until we succeed or hit test timeout.
> >>
> >
> RFC:
> 
> Base on your patch, I'm thinking to achieve a new macro TST_INFILOOP_FUNC
> which can repeat the @FUNC infinitely. Do you feel it satisfies your
> requirements to some degree or meaningful to LTP?

I'm OK with concept. I'd like more some variation of *RETRY* for name.
Comments below.

> +/**
> + * TST_INFILOOP_FUNC() - Infinitely retry a function with an increasing
> delay.
> + * @FUNC - The function which will be retried
> + * @ERET - The value returned from @FUNC on success
> + *
> + * This macro will call @FUNC in an infinite loop with a delay. If @FUNC
> + * returns @ERET then the loop exits. The delay between retries starts at
> one
> + * microsecond and is then doubled each iteration until it exceeds one
> second.
> + * When the delay exceeds one-second @FUNC keep repeat until get success
> or hit
> + * test timeout.
> + */
> +#define TST_INFILOOP_FUNC(FUNC, ERET) \
> +       TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, -1)
> +
>  #define TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, MAX_DELAY)        \
> -({     int tst_delay_ = 1;                                             \
> +({     int tst_delay_ = 1, tst_max_delay_ = MAX_DELAY;                 \
> +       if (MAX_DELAY < 0)                                              \
> +                tst_max_delay_ *= MAX_DELAY;                           \

Shouldn't this be just times (-1). For -5 you get 25 as max sleep time.

>         for (;;) {                                                      \
>                 typeof(FUNC) tst_ret_ = FUNC;                           \
>                 if (tst_ret_ == ERET)                                   \
>                         break;                                          \
> -               if (tst_delay_ < MAX_DELAY * 1000000) {                 \
> -                       usleep(tst_delay_);                             \
> +               usleep(tst_delay_);                                     \
> +               if (tst_delay_ < tst_max_delay_ * 1000000) {            \
>                         tst_delay_ *= 2;                                \
>                 } else {                                                \
> -                       tst_brk(TBROK, #FUNC" timed out");              \
> +                        if (MAX_DELAY > 0)                             \

pastebin has this condition backwards, but here it looks ok.

> +                               tst_brk(TBROK, #FUNC" timed out");      \
>                 }                                                       \
>         }                                                               \
>         ERET;                                                           \
> 
> Add pastebin to better readable: http://pastebin.test.redhat.com/805437
> 
> --
> Regards,
> Li Wang
>