Re: [LTP] [PATCH v1] readahead02.c: Use fsync instead of sync

[Wei Gao via ltp <ltp@lists.linux.it>]

On Mon, Jan 16, 2023 at 03:08:44PM +0000, Richard Palethorpe wrote:
> Hello,
> 
> Wei Gao via ltp <ltp@lists.linux.it> writes:
> 
> > Use fsync on test file instead of sync should faster than syncing
> > whole system.
> 
> The test completes in less than a second in OpenQA. We don't want to
> risk introducing a regression or spend time reviewing changes unless the
> performance improvement solves a timeout.
> 
> I suggest you convert dup06 to the new API (for example) or investigate
> a test failure.
> 
The motivation of this change is base on the https://github.com/linux-test-project/ltp/issues/972
which give following suggestion:
"As we run the test inside a loop device I guess that we can also 
sync and drop caches just for the device, which should be faster 
than syncing and dropping the whole system. Possibly we just need 
to umount it and mount it again."

But currently i can not find any API to sync and drop caches just 
ONLY for device, so base my view just replace sync whole 
system to single file also can make a small help.

> >
> > Signed-off-by: Wei Gao <wegao@suse.com>
> > ---
> >  .../kernel/syscalls/readahead/readahead02.c     | 17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
> >
> > diff --git a/testcases/kernel/syscalls/readahead/readahead02.c b/testcases/kernel/syscalls/readahead/readahead02.c
> > index 7acf4bb18..e04046bc3 100644
> > --- a/testcases/kernel/syscalls/readahead/readahead02.c
> > +++ b/testcases/kernel/syscalls/readahead/readahead02.c
> > @@ -99,6 +99,17 @@ static void drop_caches(void)
> >  	SAFE_FILE_PRINTF(DROP_CACHES_FNAME, "1");
> >  }
> >  
> > +static void sync_drop_caches(void)
> > +{
> > +	int fd;
> > +
> > +	fd  = SAFE_OPEN(testfile, O_RDONLY);
> > +	if (fsync(fd) == -1)
> > +		tst_brk(TBROK | TERRNO, "fsync()");
> > +	SAFE_CLOSE(fd);
> > +	drop_caches();
> > +}
> > +
> >  static unsigned long get_bytes_read(void)
> >  {
> >  	unsigned long ret;
> > @@ -233,8 +244,7 @@ static void test_readahead(unsigned int n)
> >  	read_testfile(tc, 0, testfile, testfile_size, &read_bytes, &usec,
> >  		      &cached);
> >  	cached_high = get_cached_size();
> > -	sync();
> > -	drop_caches();
> > +	sync_drop_caches();
> >  	cached_low = get_cached_size();
> >  	cached_max = MAX(cached_max, cached_high - cached_low);
> >  
> > @@ -246,8 +256,7 @@ static void test_readahead(unsigned int n)
> >  	else
> >  		cached = 0;
> >  
> > -	sync();
> > -	drop_caches();
> > +	sync_drop_caches();
> >  	cached_low = get_cached_size();
> >  	tst_res(TINFO, "read_testfile(1)");
> >  	ret = read_testfile(tc, 1, testfile, testfile_size, &read_bytes_ra,
> > -- 
> > 2.35.3
> 
> 
> -- 
> Thank you,
> Richard.

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