Date: Sun, 28 Jan 2018 20:02:43 +0100 From: Ingo Molnar <mingo@...nel.org> To: Andy Lutomirski <luto@...nel.org> Cc: x86@...nel.org, LKML <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Borislav Petkov <bp@...en8.de> Subject: Re: [PATCH 2/3] x86/asm: Move 'status' from thread_struct to thread_info * Andy Lutomirski <luto@...nel.org> wrote: > The TS_COMPAT bit is very hot and is accessed from code paths that > mostly also touch thread_info::flags. Move it into struct > thread_info to improve cache locality. > > The only reason it was in thread_struct is that there was a brief > period during which we didn't allow arch-specific fields in struct > thread_info. > > Linus suggested further changing: > > ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED); > > to: > > if (unlikely(ti->status & (TS_COMPAT|TS_I386_REGS_POKED))) > ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED); > > on the theory that frequently dirtying the cacheline even in pure > 64-bit code that never needs to modify status hurts performance. > That could be a reasonable followup patch, but I suspect it matters > less on top of this patch. > > Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org> > Signed-off-by: Andy Lutomirski <luto@...nel.org> > --- > arch/x86/entry/common.c | 4 ++-- > arch/x86/include/asm/processor.h | 2 -- > arch/x86/include/asm/syscall.h | 6 +++--- > arch/x86/include/asm/thread_info.h | 3 ++- > arch/x86/kernel/process_64.c | 4 ++-- > arch/x86/kernel/ptrace.c | 2 +- > arch/x86/kernel/signal.c | 2 +- > 7 files changed, 11 insertions(+), 12 deletions(-) Reviewed-by: Ingo Molnar <mingo@...nel.org> Thanks, Ingo
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