Hey Drew, On Thu, Feb 09, 2023 at 04:26:20PM +0100, 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). > > Based on riscv-linux/for-next plus the dependencies listed below. > > Dependencies: > https://lore.kernel.org/all/20230108163356.3063839-1-conor@xxxxxxxxxx/ > https://lore.kernel.org/all/20230105192610.1940841-1-heiko@xxxxxxxxx/ I've had a short (due to FOSDEM) & busy week since we discussed the automagic dependency collection. I'll try to get to it in the next few days. > The patches are also available here > https://github.com/jones-drew/linux/commits/riscv/zicboz-v4 > > To test over QEMU this branch may be used to enable Zicboz > https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz > > To test running a KVM guest with Zicboz this kvmtool branch may be used > https://github.com/jones-drew/kvmtool/commits/riscv/zicboz > > Thanks, > drew > > [1] I ported the functions under test to userspace and linked them with > a test program. Then, I ran them under gdb with a script[3] which > counted instructions by single stepping. > [2] https://lore.kernel.org/all/20221027130247.31634-1-ajones@xxxxxxxxxxxxxxxx/ > [3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60 > > v4: > - Rebased on latest for-next which allowed dropping one dependency > - Added "RISC-V: alternatives: Support patching multiple insns in assembly" > since I needed to use more than one instruction in an ALTERNATIVE call > from assembly. I can post this patch separately as a fix if desired. > - Improved the dt-binding patch commit message [Conor] > - Picked up some tags from Conor and Rob (I kept Conor's a-b on the > clear_page patch, even though there are several changes to it, because > I interpreted the a-b as "OK by me to implement a Zicboz clear_page") Yea, it was a "I am far from qualified to review your implementation, but I am okay with it existing and the remainder of the patch". Cheers, Conor.
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