lkml.org 
[lkml]   [2008]   [Aug]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] seqlock: serialize against writers
Steven Rostedt wrote:
> On Fri, 29 Aug 2008, Gregory Haskins wrote:
>
>
>> Andi Kleen wrote:
>>
>>>> Im running it on a x86_64 box as we speak. How can I tell if there is a
>>>> certain mode that is permitting this?
>>>>
>>>>
>>> If the boot up says you're running with PMtimer then it uses the fallback
>>> (usually happens on pre Fam10h AMD boxes). A typical Intel box
>>> would use the faster ring 3 only TSC path and then explode with your
>>> change I bet.
>>>
>>> Or step with gdb through gettimeofday() and see if it does a syscall.
>>>
>>> -Andi
>>>
>>>
>> It seems to be running fine with no indication it has fallen back.
>> Perhaps I need a certain workload to bring out the issue?
>>
>
> Perhaps you never hit the slow path in userland. That's the only place it
> would write. Perhaps add a dummy static variable in the fast path, and
> write to it. See if that crashes you apps.
>
> -- Steve
>

Yeah, ideas crossed in the mail ;)

I could just force all of the seqbegins to hit the slowpath by hacking
the code and see what happens (aside from slowing down, of course ;)

Question: Which seqlock_t does userspace use? I assume it uses
seqlock_t and not raw_seqlock_t. But the only reason that I ask is that
I converted raw_seqlock_t to use the new style as well to be consistent,
even though it is not strictly necessary for the same reasons. So if
perchance userspace uses the raw variant, I could solve this issue by
only re-working the seqlock_t variant. Kind of a long shot, but figured
I would mention it :)

-Greg



[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2008-08-29 18:41    [W:0.108 / U:0.360 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site