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Re: [PATCH] s390: optimize syscall function


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?

zw


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