[PATCH] s390: optimize syscall function

[Martin Schwidefsky]

On Mon, 12 Jun 2017 08:06:36 -0400
Zack Weinberg <zackw@panix.com> wrote:

> On Mon, Jun 12, 2017 at 1:49 AM, Martin Schwidefsky
> <schwidefsky@de.ibm.com> wrote:
> > On Fri,  9 Jun 2017 13:29:07 +0200
> > Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >  
> >> Since kernel 2.6.0 all Linux version accept the system call number
> >> in register 1 for svc 0. There is no need to have special handling
> >> that uses EX for system calls < 256. This will simplify and speed
> >> up that code.
> >>
> >> A microbenchmark doing "syscall(__NR_getpid);" in a loops gets faster
> >> by ~12%.
> >>
> >>         * sysdeps/unix/sysv/linux/s390/s390-64/syscall.S: Simplify
> >>         code by always using SVC 0 instead of EX.
> >>         * sysdeps/unix/sysv/linux/s390/s390-64/syscall.S: Likewise.
> >>
> >> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> >> ---
> >>  sysdeps/unix/sysv/linux/s390/s390-32/syscall.S |   12 +++---------
> >>  sysdeps/unix/sysv/linux/s390/s390-64/syscall.S |   12 +++---------
> >>  2 files changed, 6 insertions(+), 18 deletions(-)  
> >
> > NAK. E.g. this from glibc:
> >
> > sysdeps/unix/sysv/linux/s390/s390-64:  
> 
> Uh, I believe Christian was proposing to change the exact code you are
> quoting.  Did you think he was proposing to remove backward
> compatibility for EX from the kernel-side syscall path?

Indeed, I was thinking too much about the kernel side of things. 

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.