[lkml]   [2020]   [Apr]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC PATCH v2 12/13] powerpc/kernel: Do not inconditionally save non volatile registers on system call
Christophe Leroy's on April 7, 2020 4:18 am:
> Le 06/04/2020 à 03:25, Nicholas Piggin a écrit :
>> Christophe Leroy's on April 6, 2020 3:44 am:
>>> Before : 347 cycles on null_syscall
>>> After : 327 cycles on null_syscall
>> The problem I had doing this is that signal delivery wnats full regs,
>> and you don't know if you have a signal pending ahead of time if you
>> have interrupts enabled.
>> I began to try bailing out back to asm to save nvgprs and call again.
>> I think that can be made to work, but it is more complication in asm,
>> and I soon found that 64s CPUs don't care about NVGPRs too much so it's
>> nice to get rid of the !fullregs state.
> I tried a new way in v3, please have a look. I split
> syscall_exit_prepare() in 3 parts and the result is unexpected: it is
> better than before the series (307 cycles now versus 311 cycles with
> full ASM syscall entry/exit).

Great! Well I don't really see a problem with how you changed the C code
around. I'll have to look at the assembly but I don't think it would
have caused a problem for 64s.


 \ /
  Last update: 2020-04-07 02:29    [W:0.056 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site