From a7a9dcd882a67b68568868b988289fce5ffd8419 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Mon, 3 Apr 2017 16:41:02 +1000 Subject: [PATCH] powerpc: Avoid taking a data miss on every userspace instruction miss Early on in do_page_fault() we call store_updates_sp(), regardless of the type of exception. For an instruction miss this doesn't make sense, because we only use this information to detect if a data miss is the result of a stack expansion instruction or not. Worse still, it results in a data miss within every userspace instruction miss handler, because we try and load the very instruction we are about to install a pte for! A simple exec microbenchmark runs 6% faster on POWER8 with this fix: #include #include #include int main(int argc, char *argv[]) { unsigned long left = atol(argv[1]); char leftstr[16]; if (left-- == 0) return 0; sprintf(leftstr, "%ld", left); execlp(argv[0], argv[0], leftstr, NULL); perror("exec failed\n"); return 0; } Pass the number of iterations on the command line (eg 10000) and time how long it takes to execute. Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman --- arch/powerpc/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index fd6484fc2fa9..3a7d580fdc59 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -287,7 +287,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, * can result in fault, which will cause a deadlock when called with * mmap_sem held */ - if (user_mode(regs)) + if (!is_exec && user_mode(regs)) store_update_sp = store_updates_sp(regs); if (user_mode(regs))