On 04/22/2013 05:56 PM, Andi Kleen wrote:
Rik van Riel <riel@xxxxxxxxxx> writes:
If we always incremented the ticket number by 2 (instead of 1), then
we could use the lower bit of the ticket number as the spinlock.
Spinning on a single bit is very inefficient, as you need to do
try lock in a loop which is very unfriendly to the MESI state protocol.
It's much better to have at least three states and allow
spinning-while-reading-only.
This is typically very visible on systems with >2S.
Absolutely, the spinning should be read-only, until the CPU
sees that the desired bit is clear. MESI-friendly spinning
is essential.
--
All rights reversed
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
