Re: [Qemu-devel] [PATCH 00/14] trace: Add static tracing to QEMU

[Lluís]

Stefan Hajnoczi writes:

> 1. Writing the trace buffer is currently synchronous - fwrite(3) is
> used by the unlucky caller that fills up the trace buffer.  Ideally
> traces should never block and write-out would be asynchronous.  With a
> regular file I'm not sure how much of an issue this is to performance,
> since the kernel could copy the trace buffer to the page cache and
> write it out sometime later.  I've avoided adding a dedicated thread
> because it will make the code more complex - any thoughts?

I think the only reliable and non-multithreaded way to do it would be to use
aio_write(3). Then, total buffer size and the threshold to trigger an aio_write
should be tuned to match the current disk throughput in order to eliminate
emulation stalls.

But this doesn't sound much easier than a producer-consumer threading scheme.

Lluis

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