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SubjectRe: [PATCH] fix nanosleep() granularity bumps


Here is a fix for the problem that eliminates the index from the
structure. The index ALWAYS depends on the current value of
base->timer_jiffies in a rather simple way which is I exploit. Either
patch works, but this seems much simpler...

-g


Tim Schmielau wrote:
> On Tue, 18 Mar 2003, Tim Schmielau wrote:
>
>
>>Please don't yet forward to Linus. After twisting my little brain a bit
>>further, I see that the patch is still wrong if the lowest TVR_BITS of
>>INITIAL_JIFFIES happen to be zero while others are not.
>
>
> OK, this one looks ugly but should be correct, even in the case of a
> partial timer cascade on the first timer interrupt:
>
>
> --- linux-2.5.65/kernel/timer.c.orig Tue Mar 18 13:02:39 2003
> +++ linux-2.5.65/kernel/timer.c Tue Mar 18 13:41:53 2003
> @@ -1182,11 +1182,23 @@
> INIT_LIST_HEAD(base->tv1.vec + j);
>
> base->timer_jiffies = INITIAL_JIFFIES;
> - base->tv1.index = INITIAL_JIFFIES & TVR_MASK;
> - base->tv2.index = (INITIAL_JIFFIES >> TVR_BITS) & TVN_MASK;
> - base->tv3.index = (INITIAL_JIFFIES >> (TVR_BITS+TVN_BITS)) & TVN_MASK;
> - base->tv4.index = (INITIAL_JIFFIES >> (TVR_BITS+2*TVN_BITS)) & TVN_MASK;
> - base->tv5.index = (INITIAL_JIFFIES >> (TVR_BITS+3*TVN_BITS)) & TVN_MASK;
> + /*
> + * The tv indices are always larger by one compared to the
> + * respective parts of timer_jiffies. If all lower indices are
> + * zero at initialisation, this is achieved by an (otherwise
> + * unneccessary) invocation of the timer cascade on the first
> + * timer interrupt. If not, we need to take it into account
> + * here:
> + */
> + j = (base->tv1.index = INITIAL_JIFFIES & TVR_MASK) !=0;
> + j |= (base->tv2.index = ((INITIAL_JIFFIES >> TVR_BITS) + j)
> + & TVN_MASK) !=0;
> + j |= (base->tv3.index = ((INITIAL_JIFFIES >> (TVR_BITS+TVN_BITS)) + j)
> + & TVN_MASK) !=0;
> + j |= (base->tv4.index = ((INITIAL_JIFFIES >> (TVR_BITS+2*TVN_BITS)) + j)
> + & TVN_MASK) !=0;
> + base->tv5.index = ((INITIAL_JIFFIES >> (TVR_BITS+3*TVN_BITS)) + j)
> + & TVN_MASK;
> }
>
> static int __devinit timer_cpu_notify(struct notifier_block *self,
>
> -
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>

--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml
diff -urP -I '\$Id:.*Exp \$' -X /usr/src/patch.exclude linux-2.5.64-kb/kernel/timer.c linux/kernel/timer.c
--- linux-2.5.64-kb/kernel/timer.c 2003-03-05 15:10:40.000000000 -0800
+++ linux/kernel/timer.c 2003-03-18 17:59:02.000000000 -0800
@@ -44,12 +44,10 @@
#define TVR_MASK (TVR_SIZE - 1)

typedef struct tvec_s {
- int index;
struct list_head vec[TVN_SIZE];
} tvec_t;

typedef struct tvec_root_s {
- int index;
struct list_head vec[TVR_SIZE];
} tvec_root_t;

@@ -117,7 +115,7 @@
* Can happen if you add a timer with expires == jiffies,
* or you set a timer to go off in the past
*/
- vec = base->tv1.vec + base->tv1.index;
+ vec = base->tv1.vec + (base->timer_jiffies & TVR_MASK);
} else if (idx <= 0xffffffffUL) {
int i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK;
vec = base->tv5.vec + i;
@@ -351,12 +349,12 @@
#endif


-static int cascade(tvec_base_t *base, tvec_t *tv)
+static int cascade(tvec_base_t *base, tvec_t *tv, int index)
{
/* cascade all the timers from tv up one level */
struct list_head *head, *curr, *next;

- head = tv->vec + tv->index;
+ head = tv->vec + index;
curr = head->next;
/*
* We are removing _all_ timers from the list, so we don't have to
@@ -374,7 +372,7 @@
}
INIT_LIST_HEAD(head);

- return tv->index = (tv->index + 1) & TVN_MASK;
+ return index & TVN_MASK;
}

/***
@@ -384,22 +382,26 @@
* This function cascades all vectors and executes all expired timer
* vectors.
*/
+#define INDEX(N) (base->timer_jiffies >> (TVR_BITS + N * TVN_BITS)) & TVN_MASK
+
static inline void __run_timers(tvec_base_t *base)
{
+ int index = base->timer_jiffies & TVR_MASK;
spin_lock_irq(&base->lock);
+ if(jiffies - base->timer_jiffies > 0)
while ((long)(jiffies - base->timer_jiffies) >= 0) {
struct list_head *head, *curr;

/*
* Cascade timers:
*/
- if (!base->tv1.index &&
- (cascade(base, &base->tv2) == 1) &&
- (cascade(base, &base->tv3) == 1) &&
- cascade(base, &base->tv4) == 1)
- cascade(base, &base->tv5);
+ if (!index &&
+ (cascade(base, &base->tv2, INDEX(0)) == 1) &&
+ (cascade(base, &base->tv3, INDEX(1)) == 1) &&
+ cascade(base, &base->tv4, INDEX(2)) == 1)
+ cascade(base, &base->tv5, INDEX(3));
repeat:
- head = base->tv1.vec + base->tv1.index;
+ head = base->tv1.vec + index;
curr = head->next;
if (curr != head) {
void (*fn)(unsigned long);
@@ -424,7 +426,6 @@
goto repeat;
}
++base->timer_jiffies;
- base->tv1.index = (base->tv1.index + 1) & TVR_MASK;
}
#if CONFIG_SMP
base->running_timer = NULL;
@@ -1181,12 +1182,7 @@
for (j = 0; j < TVR_SIZE; j++)
INIT_LIST_HEAD(base->tv1.vec + j);

- base->timer_jiffies = INITIAL_JIFFIES;
- base->tv1.index = INITIAL_JIFFIES & TVR_MASK;
- base->tv2.index = (INITIAL_JIFFIES >> TVR_BITS) & TVN_MASK;
- base->tv3.index = (INITIAL_JIFFIES >> (TVR_BITS+TVN_BITS)) & TVN_MASK;
- base->tv4.index = (INITIAL_JIFFIES >> (TVR_BITS+2*TVN_BITS)) & TVN_MASK;
- base->tv5.index = (INITIAL_JIFFIES >> (TVR_BITS+3*TVN_BITS)) & TVN_MASK;
+ base->timer_jiffies = jiffies -1;
}

static int __devinit timer_cpu_notify(struct notifier_block *self,
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