[ Sorry for the duplicate. Andrew indicated I'd used reply-list rather
than reply-all. ]
On 1/30/23 05:01, Andrew Jones wrote:
When the Zicboz extension is available we can more rapidly zero naturally
aligned Zicboz block sized chunks of memory. As pages are always page
aligned and are larger than any Zicboz block size will be, then
clear_page() appears to be a good candidate for the extension. While cycle
count and energy consumption should also be considered, we can be pretty
certain that implementing clear_page() with the Zicboz extension is a win
by comparing the new dynamic instruction count with its current count[1].
Doing so we see that the new count is just over a quarter of the old count
(see patch4's commit message for more details).
For those of you who reviewed v1[2], you may be looking for the memset()
patches. As pointed out in v1, and a couple follow-up emails, it's not
clear that patching memset() is a win yet. When I get a chance to test
on real hardware with a comprehensive benchmark collection then I can
post the memset() patches separately (assuming the benchmarks show it's
worthwhile).
So a note. On the userspace side we are using cboz for clearing memory
in memset. While the data is intermixed with other changes, there's a
very significant drop in stores and a host of related low level
performance counters and a notable uptick in gcc #5 performance from
spec2017 which is particularly sensitive to memory clearing. We haven't
seen any performance regressions attributable to using cboz across
spec2017's integer suite.
I believe our current threshold setting is to use cboz for chunks >= 128
bytes.
Jeff
