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Date: Thu, 05 Feb 2009 12:58:15 +0300
From: Pavel Emelyanov <xemul@...nvz.org>
To: Kirill Korotaev <dev@...allels.com>, Ingo Molnar <mingo@...e.hu>
CC: Linus Torvalds <torvalds@...ux-foundation.org>,
Kirill Korotaev <dev@...nvz.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [git pull] timer fix
Kirill Korotaev wrote:
> ACK, it works. Why not save another 4 bytes of .bss then by changing
> hept_t1_cmp to u32? ;-)
Hm... .bss you say? :) The bloat-o-meter results would be:
For the original fix with casting hpet_t1_cmp to u32 inside the loop
add/remove: 0/0 grow/shrink: 1/0 up/down: 2/0 (2)
function old new delta
hpet_rtc_interrupt 741 743 +2
For the fix with casting the substitution result to s32
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-2 (-2)
function old new delta
hpet_rtc_interrupt 741 739 -2
For the proposed by Kirill type change of the hpet_t1_cmp
add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-6 (-6)
function old new delta
hpet_rtc_timer_init 186 185 -1
hpet_rtc_interrupt 741 740 -1
hpet_t1_cmp 8 4 -4
That's the fix:
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 64d5ad0..dfbbb94 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -897,7 +897,7 @@ static unsigned long hpet_rtc_flags;
static int hpet_prev_update_sec;
static struct rtc_time hpet_alarm_time;
static unsigned long hpet_pie_count;
-static unsigned long hpet_t1_cmp;
+static u32 hpet_t1_cmp;
static unsigned long hpet_default_delta;
static unsigned long hpet_pie_delta;
static unsigned long hpet_pie_limit;
Reported-by: Kirill Korotaev <dev@...nvz.org>
Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
This one also works. Should I re-send this patch in a proper way?
> Kirill
>
>
> On 2/5/09 1:58 AM, "Ingo Molnar" <mingo@...e.hu> wrote:
>
>>
>> * Linus Torvalds <torvalds@...ux-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@...nvz.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@...nvz.org>
>> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
>> Signed-off-by: Ingo Molnar <mingo@...e.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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