lkml.org 
[lkml]   [2013]   [Aug]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer
Date
Hi Steven,

On Thu, 22 Aug 2013 21:08:30 -0400, Steven Rostedt wrote:
> On Fri, 23 Aug 2013 07:57:15 +0800
> "zhangwei(Jovi)" <jovi.zhangwei@huawei.com> wrote:
>
>
>> >
>> > What about creating a per cpu buffer when uprobes are registered, and
>> > delete them when they are finished? Basically what trace_printk() does
>> > if it detects that there are users of trace_printk() in the kernel.
>> > Note, it does not deallocate them when finished, as it is never
>> > finished until reboot ;-)
>> >
>> > -- Steve
>> >
>> I also thought out this approach, but the issue is we cannot fetch user
>> memory into per-cpu buffer, because use per-cpu buffer should under
>> preempt disabled, and fetching user memory could sleep.
>
> Actually, we could create a per_cpu mutex to match the per_cpu buffers.
> This is not unlike what we do in -rt.
>
> int cpu;
> struct mutex *mutex;
> void *buf;
>
>
> /*
> * Use per cpu buffers for fastest access, but we might migrate
> * So the mutex makes sure we have sole access to it.
> */
>
> cpu = raw_smp_processor_id();
> mutex = per_cpu(uprobe_cpu_mutex, cpu);
> buf = per_cpu(uprobe_cpu_buffer, cpu);
>
> mutex_lock(mutex);
> store_trace_args(..., buf,...);
> mutex_unlock(mutex);
>

Great! I'll go with this approach. Is it OK to you, Masami?

Thanks,
Namhyung


\
 
 \ /
  Last update: 2013-08-27 10:21    [W:0.956 / U:0.024 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site