Josh Boyer wrote:
On Wed, 20 Aug 2008 14:06:51 -0500
Hollis Blanchard <hollisb@xxxxxxxxxx> wrote:
To be honest I unfortunately don't know how big the impact for
non-virtualized systems is. I would like to test it, but without
hardware performance counters on the core I have I'm not sure (yet)
how
to measure that in a good way - any suggestion welcome.
I don't see why we need performance counters. Can't we just compare any
bare metal benchmark results with the patch both applied and not?
Do you know of one that causes a large amount of
local_irq_{disable,enable}s to be called?
I think *every* workload causes a large number of
local_irq_{disable,enable} calls... :)
Well, sure. I was just going for "test the change as specifically as
possible." One could write a module that did X number of
disable/enable pairs and reported the timebase at start and end to
compare. X could even be a module parameter. Just to try and
eliminate noise or whatever from the testing.
/me shrugs.
josh
yeah I thought of something like that too, because I expect the
difference to be very small.
Instead of a module I wanted to put this somewhere prior to the kernel
mounting root-fs to avoid interferences from whatever userspace is doing
(e.g. causing thousands of interrupts come back while the module
perform that test.).
Eventually we need a synthetic benchmark like that AND a check how it
affects a common system to be sure.
--
Grüsse / regards,
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization
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