> -----Original Message----- > From: gregkh@xxxxxxxxxxxxxxxxxxx [mailto:gregkh@xxxxxxxxxxxxxxxxxxx] > Sent: Thursday, September 28, 2017 4:18 PM > To: Ruxandra Ioana Radulescu <ruxandra.radulescu@xxxxxxx> > Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>; > devel@xxxxxxxxxxxxxxxxxxxx; arnd@xxxxxxxx; stuyoder@xxxxxxxxx; Roy > Pledge <roy.pledge@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; > agraf@xxxxxxx; Bogdan Purcareata <bogdan.purcareata@xxxxxxx>; > Laurentiu Tudor <laurentiu.tudor@xxxxxxx> > Subject: Re: [PATCH] staging: fsl-mc/dpio: Fix incorrect comparison > > On Thu, Sep 28, 2017 at 01:07:48PM +0000, Ruxandra Ioana Radulescu wrote: > > > -----Original Message----- > > > From: Dan Carpenter [mailto:dan.carpenter@xxxxxxxxxx] > > > Sent: Thursday, September 28, 2017 3:49 PM > > > To: Ruxandra Ioana Radulescu <ruxandra.radulescu@xxxxxxx> > > > Cc: gregkh@xxxxxxxxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxx; > > > arnd@xxxxxxxx; stuyoder@xxxxxxxxx; Roy Pledge > <roy.pledge@xxxxxxx>; > > > linux-kernel@xxxxxxxxxxxxxxx; agraf@xxxxxxx; Bogdan Purcareata > > > <bogdan.purcareata@xxxxxxx>; Laurentiu Tudor > > > <laurentiu.tudor@xxxxxxx> > > > Subject: Re: [PATCH] staging: fsl-mc/dpio: Fix incorrect comparison > > > > > > On Wed, Sep 27, 2017 at 12:57:28PM -0500, Ioana Radulescu wrote: > > > > diff --git a/drivers/staging/fsl-mc/bus/dpio/dpio-service.c > > > b/drivers/staging/fsl-mc/bus/dpio/dpio-service.c > > > > index f809682..26922fc 100644 > > > > --- a/drivers/staging/fsl-mc/bus/dpio/dpio-service.c > > > > +++ b/drivers/staging/fsl-mc/bus/dpio/dpio-service.c > > > > @@ -76,7 +76,7 @@ static inline struct dpaa2_io > > > *service_select_by_cpu(struct dpaa2_io *d, > > > > if (d) > > > > return d; > > > > > > > > - if (unlikely(cpu >= num_possible_cpus())) > > > > + if (unlikely(cpu >= (int)num_possible_cpus())) > > > > > > > > > Drivers shouldn't use likely/unlikley. > > > > I was under the impression it's ok to use them on hotpath > > (and while not entirely obvious, this function is called on > > other drivers' hotpath). > > Only use it if you can measure the difference. If you can not, then do > not use it as the compiler and the CPU will guess it better than you > will. > > This has been proven many times, something like 80% of our > likely/unlikely usage in the kernel is wrong because of this, see the > work from Andi Kleen many years ago in this area. > > So please remove it. Unless you can prove it matters, and if so, > document that. Greg, thanks for the explanation. Will remove it in v2. Ioana _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
