Messages in this thread | | | From | Alexander Shishkin <> | Subject | Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow tracing units | Date | Thu, 19 Dec 2013 13:17:51 +0200 |
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Peter Zijlstra <peterz@infradead.org> 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.
> Also, 'some implementations', that sounds like a fail right there. Why > are there already different implementations, and some which such stupid > design, of something this new? > > How about just saying NO to the ones that requires physically contiguous > allocations?
No reason to leave those out, because they are still extremely useful for tracing and fit perfectly fine in a model with two buffers.
Regards, -- Alex
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