Messages in this thread Patch in this message | | | Date | Mon, 18 Jun 2007 10:31:09 +0200 | From | Ingo Molnar <> | Subject | Re: [BUG] long freezes on thinkpad t60 |
| |
(Ravikiran Cc:-ed too)
* Miklos Szeredi <miklos@szeredi.hu> wrote:
> > To test this theory, could you try the patch below, does this fix > > your hangs too? > > Not tried yet, but obviously it does, since it's a superset of the > previous fix. I could try without the smb_mb(), but see below.
oops - the 64-bit processor.h bits were included by accident - updated patch below.
> > This change causes the memory access of the "easy" spin-loop portion > > to be more agressive: after the REP; NOP we'd not do the 'easy-loop' > > with a simple CMPB, but we'd re-attempt the atomic op. > > It looks as if this is going to overflow of the lock counter, no?
hm, what do you mean? There's no lock counter.
Ingo
--------------------------> Subject: [patch] x86: fix spin-loop starvation bug From: Ingo Molnar <mingo@elte.hu>
Miklos Szeredi reported very long pauses (several seconds, sometimes more) on his T60 (with a Core2Duo) which he managed to track down to wait_task_inactive()'s open-coded busy-loop. He observed that an interrupt on one core tries to acquire the runqueue-lock but does not succeed in doing so for a very long time - while wait_task_inactive() on the other core loops waiting for the first core to deschedule a task (which it wont do while spinning in an interrupt handler).
The problem is: both the spin_lock() code and the wait_task_inactive() loop uses cpu_relax()/rep_nop(), so in theory the CPU should have guaranteed MESI-fairness to the two cores - but that didnt happen: one of the cores was able to monopolize the cacheline that holds the runqueue lock, for extended periods of time.
This patch changes the spin-loop to assert an atomic op after every REP NOP instance - this will cause the CPU to express its "MESI interest" in that cacheline after every REP NOP.
Signed-off-by: Ingo Molnar <mingo@elte.hu> --- include/asm-i386/spinlock.h | 16 ++++------------ include/asm-x86_64/spinlock.h | 15 +++------------ 2 files changed, 7 insertions(+), 24 deletions(-)
Index: linux-cfs-2.6.22-rc5.q/include/asm-i386/spinlock.h =================================================================== --- linux-cfs-2.6.22-rc5.q.orig/include/asm-i386/spinlock.h +++ linux-cfs-2.6.22-rc5.q/include/asm-i386/spinlock.h @@ -37,10 +37,7 @@ static inline void __raw_spin_lock(raw_s asm volatile("\n1:\t" LOCK_PREFIX " ; decb %0\n\t" "jns 3f\n" - "2:\t" - "rep;nop\n\t" - "cmpb $0,%0\n\t" - "jle 2b\n\t" + "rep; nop\n\t" "jmp 1b\n" "3:\n\t" : "+m" (lock->slock) : : "memory"); @@ -65,21 +62,16 @@ static inline void __raw_spin_lock_flags "testl $0x200, %[flags]\n\t" "jz 4f\n\t" STI_STRING "\n" - "3:\t" - "rep;nop\n\t" - "cmpb $0, %[slock]\n\t" - "jle 3b\n\t" + "rep; nop\n\t" CLI_STRING "\n\t" "jmp 1b\n" "4:\t" - "rep;nop\n\t" - "cmpb $0, %[slock]\n\t" - "jg 1b\n\t" + "rep; nop\n\t" "jmp 4b\n" "5:\n\t" : [slock] "+m" (lock->slock) : [flags] "r" (flags) - CLI_STI_INPUT_ARGS + CLI_STI_INPUT_ARGS : "memory" CLI_STI_CLOBBERS); } #endif Index: linux-cfs-2.6.22-rc5.q/include/asm-x86_64/spinlock.h =================================================================== --- linux-cfs-2.6.22-rc5.q.orig/include/asm-x86_64/spinlock.h +++ linux-cfs-2.6.22-rc5.q/include/asm-x86_64/spinlock.h @@ -28,10 +28,7 @@ static inline void __raw_spin_lock(raw_s "\n1:\t" LOCK_PREFIX " ; decl %0\n\t" "jns 2f\n" - "3:\n" - "rep;nop\n\t" - "cmpl $0,%0\n\t" - "jle 3b\n\t" + "rep; nop\n\t" "jmp 1b\n" "2:\t" : "=m" (lock->slock) : : "memory"); } @@ -49,16 +46,10 @@ static inline void __raw_spin_lock_flags "testl $0x200, %1\n\t" /* interrupts were disabled? */ "jz 4f\n\t" "sti\n" - "3:\t" - "rep;nop\n\t" - "cmpl $0, %0\n\t" - "jle 3b\n\t" + "rep; nop\n\t" "cli\n\t" "jmp 1b\n" - "4:\t" - "rep;nop\n\t" - "cmpl $0, %0\n\t" - "jg 1b\n\t" + "rep; nop\n\t" "jmp 4b\n" "5:\n\t" : "+m" (lock->slock) : "r" ((unsigned)flags) : "memory"); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |