Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow tracing units

[Alexander Shishkin]

Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:

> On Thu, Dec 19, 2013 at 01:17:51PM +0200, Alexander Shishkin wrote:
>> Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
>> 
>> > On Thu, Dec 19, 2013 at 09:53:44AM +0200, Alexander Shishkin wrote:
>> >> Yes and some implementations of PT have the same issue, but you can do a
>> >> sufficiently large high order allocation and map it to userspace and
>> >> still no copying (or parsing/decoding) in kernel space required.
>> >
>> > What's sufficiently large? The largest we could possibly allocate is
>> > something like 4k^11 which is 8M or so. That's not all that big given
>> > you keep saying it generates in the order of 100 MB/s.
>> 
>> One chunk is 8M. You can have as many as the buddy allocator permits you
>> to have. When you get a PMI, you simply switch one chunk for another and
>> on the tracing goes.
>
> This document you referred me to looks to specify something with a
> proper s/g implementation; called ToPA. There doesn't appear to be a
> limit to the linked entries and you can specify a size per entry, and I
> don't see anywhere why 4k would be bad.

JFYI, 11.2.4.1, "Single Output Region ToPA Implementation".

Regards,
--
Alex
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