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SubjectRe: [git pull] timer fix

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> } while ((s32)(hpet_readl(HPET_COUNTER) - hpet_t1_cmp) > 0);

that is also more efficient code by 6 bytes:

before:

ffffffff81020856: ff c3 inc %ebx
ffffffff81020858: 48 05 f0 00 00 00 add $0xf0,%rax
ffffffff8102085e: 8b 00 mov (%rax),%eax
ffffffff81020860: 8b 15 2a 79 85 00 mov 0x85792a(%rip),%edx # ffffffff81878190 <hpet_t1_cmp>
ffffffff81020866: 89 c0 mov %eax,%eax
ffffffff81020868: 48 29 d0 sub %rdx,%rax
ffffffff8102086b: 48 85 c0 test %rax,%rax
ffffffff8102086e: 7f bf jg ffffffff8102082f <hpet_rtc_interrupt+0x68>
ffffffff81020870: 85 db test %ebx,%ebx
after:

ffffffff81020856: ff c3 inc %ebx
ffffffff81020858: 48 05 f0 00 00 00 add $0xf0,%rax
ffffffff8102085e: 8b 00 mov (%rax),%eax
ffffffff81020860: 2b 05 2a 79 85 00 sub 0x85792a(%rip),%eax # ffffffff81878190 <hpet_t1_cmp>
ffffffff81020866: 85 c0 test %eax,%eax
ffffffff81020868: 7f c5 jg ffffffff8102082f <hpet_rtc_interrupt+0x68>
ffffffff8102086a: 85 db test %ebx,%ebx
Kirill, Pavel, could you please re-test the updated commit attached below?

Ingo

---------------->
From 66a36a1e95fe9de9c6a56f0bcd01f4ba21929f86 Mon Sep 17 00:00:00 2001
From: Pavel Emelyanov <xemul@openvz.org>
Date: Wed, 4 Feb 2009 13:40:31 +0300
Subject: [PATCH] x86: fix hpet timer reinit for x86_64
There's a small problem with hpet_rtc_reinit function - it checks
for the:

hpet_readl(HPET_COUNTER) - hpet_t1_cmp > 0
to continue increasing both the HPET_T1_CMP (register) and the
hpet_t1_cmp (variable).

But since the HPET_COUNTER is always 32-bit, if the hpet_t1_cmp
is 64-bit this condition will always be FALSE once the latter hits
the 32-bit boundary, and we can have a situation, when we don't
increase the HPET_T1_CMP register high enough.

The result - timer stops ticking, since HPET_T1_CMP becomes less,
than the COUNTER and never increased again.

The solution is (based on Linus's suggestion) to compare 64-bits
(on 64-bit x86), but to do the comparison on 32-bit signed
integers.

Reported-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/hpet.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 64d5ad0..c761f91 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -1075,7 +1075,7 @@ static void hpet_rtc_timer_reinit(void)
hpet_t1_cmp += delta;
hpet_writel(hpet_t1_cmp, HPET_T1_CMP);
lost_ints++;
- } while ((long)(hpet_readl(HPET_COUNTER) - hpet_t1_cmp) > 0);
+ } while ((s32)(hpet_readl(HPET_COUNTER) - hpet_t1_cmp) > 0);

if (lost_ints) {
if (hpet_rtc_flags & RTC_PIE)

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