> On Apr 23, 2019, at 10:23 AM, Andy Lutomirski <l...@kernel.org> wrote: > > On Tue, Apr 23, 2019 at 9:56 AM Nadav Amit <na...@vmware.com> wrote: >>> On Apr 23, 2019, at 9:50 AM, Andy Lutomirski <l...@kernel.org> wrote: >>> >>> On Tue, Apr 23, 2019 at 12:12 AM Nadav Amit <na...@vmware.com> wrote: >> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Fluto%2Flinux.git%2Flog%2F%3Fh%3Dx86%2Ffixes&data=02%7C01%7Cnamit%40vmware.com%7Cb0ba13a059b54abcb1c008d6c8107a54%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636916370442070349&sdata=5uXX95CD%2FAI5ZSJON%2BjCAKQ88sAwZgme6Az0ZHpEGZo%3D&reserved=0 >> >> Remove flush_tlb_info variables from the stack. This allows to align >>>> flush_tlb_info to cache-line and avoid potentially unnecessary cache >>>> line movements. It also allows to have a fixed virtual-to-physical >>>> translation of the variables, which reduces TLB misses. >>>> >>>> Use per-CPU struct for flush_tlb_mm_range() and >>>> flush_tlb_kernel_range(). Add debug assertions to ensure there are >>>> no nested TLB flushes that might overwrite the per-CPU data. For >>>> arch_tlbbatch_flush(), use a const struct. >>>> >>>> Results when running a microbenchmarks that performs 10^6 MADV_DONTEED >>>> operations and touching a page, in which 3 additional threads run a >>>> busy-wait loop (5 runs): >>> >>> Can you add a memset(,,,. 0, sizeof(struct flush_tlb_info)) everywhere >>> you grab it? Or, even better, perhaps do something like: >>> >>> static inline struct flush_tlb_info *get_flush_tlb_info(void) >>> { >>> /* check reentrancy, make sure that we use smp_processor_id() or >>> otherwise assert that we're bound to a single CPU. */ >>> struct flush_tlb_info *ptr = this_cpu_ptr(...); >>> memset(ptr, 0, sizeof(*ptr)); >>> return ptr; >>> } >>> >>> static inline void put_flush_tlb_info(void) >>> { >>> /* finish checking reentrancy. */ >>> } >> >> I’ll check if the compiler is smart enough to avoid redundant assignments, >> and if it is not, I’ll just give all the struct arguments to >> get_flush_tlb_info() instead of memset() if you don’t mind. > > Sounds good. > >> I also want to give a try for parallelizing the remote and local >> invocations, which really annoys me every time I look at the code. > > Yes please!
I have written some patches and they do provide a considerable performance improvement of (>10%) for remote TLB flushes. There are still some issues that need to be resolved, specifically a small slowdown for local TLB flushes (~15ns). Anyhow, based on my past experience, I will do this change in a separate patch-set after the flush_tlb_info off-stack patch makes it through.