[lkml]   [2008]   [Nov]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: debugctl msr

On Fri, Nov 21, 2008 at 9:22 AM, Metzger, Markus T
<> wrote:
>>-----Original Message-----
>>From: stephane eranian []
>>Sent: Donnerstag, 20. November 2008 22:19
>>To: Markus Metzger
>>- in ds_put_context(), you need to mark task->thread.ds_ctx = NULL or
>>this_system_context = NULL when you are
>> done, otherwise a subsequent session on the same task or CPU will
>>think there is already a context allocated but
>> the pointer will be stale.
> This should happen in:
> *(context->this) = NULL;
Ah, I missed that. I admit this code is hard to follow. Maybe it would easier to
explicitly use the actual fields.
>>- in ptrace.c:ptrace_disable(), you systematically invoke ds_release()
>>without checking if TIF_BTS_TRACE_TS
>> is set. That causes extraneous calls to ds_release() which messes up
>>the reference counting if PEBS is in use.
> That TIF only triggers the recording of scheduling timestamps.
> That ds_release_bts() call should:
> - get the context
> - fail the ownership validation in ds_validate()
> - put the context
> If ds_validate() is disabled, it would put the context twice.
Yes, that was my case.

> I am currently working on a patch to replace the validation
> mechanism by using a handle returned from ds_request().
Yes, that's the solution.

> I also added the interrupt threshold to the parameters of ds_request().
> It will be fix for one tracing session, if that's OK with you.

I found the reason why in system-wide my kernel was crashing.
It was due to the way you are writing DS_AREA_MSR in

if (!task || (task == current))
wrmsr(MSR_IA32_DS_AREA, (unsigned long)context->ds, 0);

This does not work in 64-bit, you truncate the DS address. You must use wrmsrl()
and let the macro break it down in two halves.

I am still seeing an issue whereby I have a buffer with > 100 entries
but I get an interrupt
or each sample, which is wrong. I am investigating why this is. There
should only be one
interrupt per buffer full. This use to work with my old ways of handling PEBS.


 \ /
  Last update: 2008-11-21 09:51    [W:0.074 / U:7.864 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site