linux-kernel - Re: [PATCH v1 03/11] perf: Allow for multiple ring buffers per event

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 08 May 2014 12:08:58 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v1 03/11] perf: Allow for multiple ring buffers per event

Alexander Shishkin <alexander.shishkin@...ux.intel.com> writes:

> Peter Zijlstra <peterz@...radead.org> writes:
>
>> How about something like this for the itrace thing?
>
> It's much nicer than the page swizzling draft I was about to send you.
>
>> You would mmap() the regular buffer; when write ->aux_{offset,size} in
>> the control page. After which you can do a second mmap() with the .pgoff
>> matching the aux_offset you gave and .length matching the aux_size you
>> gave.
>
> Why do we need aux_{offset,size} at all, then? Userspace should know how
> they mmap()ed it.
>
>> This way the mmap() content still looks like a single linear file (could
>> be sparse if you leave a hole, although we could require the aux_offset
>> to match the end of the data section).
>>
>> And there is still the single event->rb, not more.
>
> Fair enough.
>
>> Then, when data inside that aux data store changes they should inject an
>> PERF_RECORD_AUX to indicate this did happen, which ties it back into the
>> normal event flow.
>>
>> With this there should be no difficult page table tricks or anything.
>
> True.
>
>> The patch is way incomplete but should sketch enough of the idea..
>
> Can I take it over?
>
>> So the aux_head/tail values should also be in the file space and not
>> start at 0 again, similar for the offsets in the AUX record.
>
> With PERF_RECORD_AUX carrying offset and size, we shouldn't need
> aux_{head,tail} either, don't you think?

I take this one back, as perf record doesn't actually parse records from
the buffer, it would still need the pointers.

Regards,
--
Alex
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/