[LTP] [PATCH 1/1] readahead02: Sleep 1.5 msec to fix problem on bare metal

[Cyril Hrubis]

Hi!
> diff --git a/testcases/kernel/syscalls/readahead/readahead02.c b/testcases/kernel/syscalls/readahead/readahead02.c
> index f007db187..a2118c5ab 100644
> --- a/testcases/kernel/syscalls/readahead/readahead02.c
> +++ b/testcases/kernel/syscalls/readahead/readahead02.c
> @@ -39,6 +39,7 @@ static char testfile[PATH_MAX] = "testfile";
>  #define MEMINFO_FNAME "/proc/meminfo"
>  #define PROC_IO_FNAME "/proc/self/io"
>  #define DEFAULT_FILESIZE (64 * 1024 * 1024)
> +#define SHORT_SLEEP_US 5000
 
>  static size_t testfile_size = DEFAULT_FILESIZE;
>  static char *opt_fsizestr;
> @@ -173,6 +174,38 @@ static int read_testfile(struct tcase *tc, int do_readahead,
> 
>                         i++;
>                         offset += readahead_length;
> +
> +                       /*
> +                        * We assume that the worst case I/O speed is around
> +                        * 5MB/s which is roughly 5 bytes per 1 us, which gives
> +                        * us upper bound for retries that is readahead_size/(5
> +                        * SHORT_SLEEP_US).
> +                        *
> +                        * We also monitor the cache size increases before and
> +                        * after the sleep. With the same assumption about the
> +                        * speed we are supposed to read at least 5 * SHORT_SLEEP_US
> +                        * during that time. That amound is genreally quite close
> +                        * a page size so that we just assume
                                                               ^
			    that we sould continue as long as the cache
			    increases.
> +                        *
> +                        * Of course all of this is inprecise on multitasking
> +                        * OS however even on a system where there are several
> +                        * processes figthing for I/O this loop will wait as
> +                        * long a cache is increasing which will gives us high
> +                        * chance of waiting for the readahead to happen.
> +                        */
> +                       int retries = readahead_size / (5 * SHORT_SLEEP_US);
> +                       unsigned long cached_prev, cached_cur = get_cached_size();
> +
> +                       do {
> +                               usleep(SHORT_SLEEP_US);
> +
> +                               cached_prev = cached_cur;
> +                               cached_cur = get_cached_size();
> +
> +                               if (cached_cur <= cached_prev)
> +                                       break;
> +                       } while (retries-- > 0);
> +
>                 } while ((size_t)offset < fsize);
>                 tst_res(TINFO, "readahead calls made: %zu", i);
>                 *cached = get_cached_size();

-- 
Cyril Hrubis
chrubis@suse.cz