lkml.org 
[lkml]   [2016]   [Apr]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v4 0/10] x86/xsaves: Fix XSAVES known issues
From
Date
On 04/29/2016 01:25 PM, Andy Lutomirski wrote:
> On Fri, Apr 29, 2016 at 1:07 PM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>> On Fri, Apr 29, 2016 at 01:03:43PM -0700, Dave Hansen wrote:
>>> That's not feasible. Think of dynamic libraries or just-in-time
>>> compilers. What instruction set does /usr/bin/java use, for instance? :)
>>
>> The java argument is true. In that case or when the bitmask is
>> missing, we can allocate for all supported features.
>
> I actually want to see us moving in the direction of unconditionally
> allocating everything on process startup. If we can stop using CR0.TS
> entirely, I think everything will be better.

We can absolutely allocate the worst-case XSAVE buffer at task startup
for folks that never want to see a latency spike in the life of the app
no matter what.

But I also think it would be pretty nice if 'ls' didn't pay the 2k cost
to have AVX-512 state if it's not using AVX-512. We also don't have to
do this with CR0.TS. We'd actually use a combination of out-of-line
(not appended to task_struct) XSAVE buffers and XGETBV1 to check the
size of our XSAVE buffer before we call XSAVE* and resize it when needed.

Maybe nobody will ever care enough about 2kbytes/thread, though.

\
 
 \ /
  Last update: 2016-04-29 23:01    [W:0.198 / U:0.864 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site