Subject: Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads

From: Phil Sutter <[email-masked]>
Date: Fri, 28 Aug 2015 13:13:20 +0200

On Fri, Aug 28, 2015 at 01:09:29PM +0200, Thomas Graf wrote:
> On 08/28/15 at 12:28pm, Phil Sutter wrote:
> > After adding cond_resched() calls to threadfunc(), a surprisingly high
> > rate of insert failures occurred probably due to table resizes getting a
> > better chance to run in background. To not soften up the remaining
> > tests, retry inserts until they either succeed or fail permanently.
> > 
> > Signed-off-by: Phil Sutter <[email-masked]>
> > ---
> >  lib/test_rhashtable.c | 13 +++++++------
> >  1 file changed, 7 insertions(+), 6 deletions(-)
> > 
> > diff --git a/lib/test_rhashtable.c b/lib/test_rhashtable.c
> > index 63654e3..093cf84 100644
> > --- a/lib/test_rhashtable.c
> > +++ b/lib/test_rhashtable.c
> > @@ -244,7 +244,7 @@ static int thread_lookup_test(struct thread_data *tdata)
> >  
> >  static int threadfunc(void *data)
> >  {
> > -	int i, step, err = 0, insert_fails = 0;
> > +	int i, step, err = 0, retries = 0;
> >  	struct thread_data *tdata = data;
> >  
> >  	up(&prestart_sem);
> > @@ -253,21 +253,22 @@ static int threadfunc(void *data)
> >  
> >  	for (i = 0; i < entries; i++) {
> >  		tdata->objs[i].value = (tdata->id << 16) | i;
> > +insert_retry:
> >  		cond_resched();
> >  		err = rhashtable_insert_fast(&ht, &tdata->objs[i].node,
> >  		                             test_rht_params);
> >  		if (err == -ENOMEM || err == -EBUSY) {
> > -			tdata->objs[i].value = TEST_INSERT_FAIL;
> > -			insert_fails++;
> > +			retries++;
> > +			goto insert_retry;
> 
> Is it safe to retry indefinitely on ENOMEM? Retrying on EBUSY is
> definitely an improvement and we should do the same in the non
> threaded test as well.

Oh yes, that is definitely a bug. I will respin and add the same for the
normal test, too.

Thanks, Phil