Messages in this thread | | | Date | Fri, 3 Apr 2009 13:29:00 +0200 | From | Ingo Molnar <> | Subject | Re: [patch 01/18] x86, bts: fix race when bts tracer is removed |
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* Metzger, Markus T <markus.t.metzger@intel.com> wrote:
> >-----Original Message----- > >From: Ingo Molnar [mailto:mingo@elte.hu] > >Sent: Thursday, April 02, 2009 8:45 PM > >To: Metzger, Markus T > >Cc: tglx@linutronix.de; hpa@zytor.com; markus.t.metzger@gmail.com; roland@redhat.com; > >eranian@googlemail.com; oleg@redhat.com; Villacis, Juan; ak@linux.jf.intel.com; linux- > >kernel@vger.kernel.org > >Subject: Re: [patch 01/18] x86, bts: fix race when bts tracer is removed > > > > > >* markus.t.metzger@intel.com <markus.t.metzger@intel.com> wrote: > > > >> +static inline void ds_take_timestamp(struct ds_context *context, > >> + enum bts_qualifier qualifier, > >> + struct task_struct *task) > >> +{ > >> + struct bts_tracer *tracer = context->bts_master; > >> + barrier(); > > > >why the barrier()? > > See http://lkml.org/lkml/2009/3/31/544 > > Oleg: "In theory, we need barrier() after reading ->bts_master. > > (actually, I did see the bug reports when the compiler read the pointer > twice with the code like above)."
Please convert this piece of non-trivial information into a small two-sentence blurb and put it into a comment block.
> >struct bts_struct ts = { > > .qualifier = qualifier, > > .variant.event.jiffies = jiffies_64, > > .variant.event.pid = task->pid > >}; > > > >Also, raw use of jiffies_64 is buggy and racy. Why does this use > >jiffies to begin with - why not some finer grained time? > > What would be a good time to use?
ktime_get() would be the primary candidate. (Or, perhaps, if performance is really an issue then trace_clock() or trace_clock_global().)
Ingo
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