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

[Andi Kleen]

> > The other big problem is scalability. Even if it was somehow possible
> > to make this scheme work the IPIs for flushing would kill performance 
> > on any multi threaded client.  Given perf is not multi-threaded today, but
> > it doesn't seem a good idea to design the interface assuming no client ever
> > will be.
> 
> Well any mmap()ed interface that wants to swap buffers will have this
> same problem.

There's no need to swap buffers in a sane design. The perf ring buffer
or the ftrace buffer don't need this. There's no need for a PT buffer
to do so either. 

> 
> You can restrict the TLB flushing to the threads that poll() on the
> relevant events. This just means other threads will see old/partial
> data, but that shouldn't be a problem as they shouldn't be looking in
> the first place.

Then we get incoherent processes. You're not serious about that are you?

-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/