On Tue, Aug 11, 2015 at 3:18 PM, Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote: > On Tue, Jul 07, 2015 at 03:53:29AM -0700, tip-bot for Andy Lutomirski wrote: >> Commit-ID: 02bc7768fe447ae305e924b931fa629073a4a1b9 >> Gitweb: http://git.kernel.org/tip/02bc7768fe447ae305e924b931fa629073a4a1b9 >> Author: Andy Lutomirski <luto@xxxxxxxxxx> >> AuthorDate: Fri, 3 Jul 2015 12:44:31 -0700 >> Committer: Ingo Molnar <mingo@xxxxxxxxxx> >> CommitDate: Tue, 7 Jul 2015 10:59:08 +0200 >> >> x86/asm/entry/64: Migrate error and IRQ exit work to C and remove old assembly code >> >> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> >> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> >> Cc: Borislav Petkov <bp@xxxxxxxxx> >> Cc: Brian Gerst <brgerst@xxxxxxxxx> >> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> >> Cc: Denys Vlasenko <vda.linux@xxxxxxxxxxxxxx> >> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> >> Cc: H. Peter Anvin <hpa@xxxxxxxxx> >> Cc: Kees Cook <keescook@xxxxxxxxxxxx> >> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> >> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> >> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> >> Cc: Rik van Riel <riel@xxxxxxxxxx> >> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> >> Cc: paulmck@xxxxxxxxxxxxxxxxxx >> Link: http://lkml.kernel.org/r/60e90901eee611e59e958bfdbbe39969b4f88fe5.1435952415.git.luto@xxxxxxxxxx >> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> >> --- >> arch/x86/entry/entry_64.S | 64 +++++++++++----------------------------- >> arch/x86/entry/entry_64_compat.S | 5 ++++ >> 2 files changed, 23 insertions(+), 46 deletions(-) >> >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >> index 83eb63d..168ee26 100644 >> --- a/arch/x86/entry/entry_64.S >> +++ b/arch/x86/entry/entry_64.S >> @@ -508,7 +508,16 @@ END(irq_entries_start) >> >> testb $3, CS(%rsp) >> jz 1f >> + >> + /* >> + * IRQ from user mode. Switch to kernel gsbase and inform context >> + * tracking that we're in kernel mode. >> + */ >> SWAPGS >> +#ifdef CONFIG_CONTEXT_TRACKING >> + call enter_from_user_mode >> +#endif > > There have been a lot of patches going there lately so I couldn't follow > everything and since you just started a discussion on context tracking, I > just had a look on the latest change. > > So it seems we're now calling user_exit() on IRQ entry. This is not something > we want. We already have everything we need with rcu_irq_enter() and > vtime_account_irq_enter(). user_exit() brings a lot of overhead here that we > don't need. Plus this is called unconditionally since CONFIG_CONTEXT_TRACKING=y > on most distros now. > > We really want the context tracking code to be called on syscall slow path only > (and exceptions with static keys but an exception slow path would be desired as well). Can you explain to me what context tracking does that rcu_irq_enter and vtime_account_irq_enter don't do that's expensive? Frankly, I'd rather drop everything except the context tracking callback. We also need this for the deletion of exception_enter from the trap entries to be correct. Like I said in the other thread, there are too many hooks for arch code to juggle. Grumble. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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