Messages in this thread | | | Date | Mon, 04 May 2015 07:55:07 +0200 | From | Juergen Gross <> | Subject | Re: [PATCH 0/6] x86: reduce paravirtualized spinlock overhead |
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On 04/30/2015 06:39 PM, Jeremy Fitzhardinge wrote: > On 04/30/2015 03:53 AM, Juergen Gross wrote: >> Paravirtualized spinlocks produce some overhead even if the kernel is >> running on bare metal. The main reason are the more complex locking >> and unlocking functions. Especially unlocking is no longer just one >> instruction but so complex that it is no longer inlined. >> >> This patch series addresses this issue by adding two more pvops >> functions to reduce the size of the inlined spinlock functions. When >> running on bare metal unlocking is again basically one instruction. > > Out of curiosity, is there a measurable difference?
I did a small measurement of the pure locking functions on bare metal without and with my patches.
spin_lock() for the first time (lock and code not in cache) dropped from about 600 to 500 cycles.
spin_unlock() for first time dropped from 145 to 87 cycles.
spin_lock() in a loop dropped from 48 to 45 cycles.
spin_unlock() in the same loop dropped from 24 to 22 cycles.
Juergen
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