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Re: [PATCH] s390: optimize syscall function
- From: Zack Weinberg <zackw at panix dot com>
- To: Martin Schwidefsky <schwidefsky at de dot ibm dot com>
- Cc: Christian Borntraeger <borntraeger at de dot ibm dot com>, Stefan Liebler <stli at linux dot vnet dot ibm dot com>, Andreas Krebbel <krebbel at linux dot vnet dot ibm dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Mon, 12 Jun 2017 08:06:36 -0400
- Subject: Re: [PATCH] s390: optimize syscall function
- Authentication-results: sourceware.org; auth=none
- References: <1497007747-191015-1-git-send-email-borntraeger@de.ibm.com> <20170612074958.71090d0f@mschwideX1>
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