On Wed, 12 Sep 2007 04:12:00 -0700 (PDT)
David Miller <[EMAIL PROTECTED]> wrote:
> From: Eric Dumazet <[EMAIL PROTECTED]>
> Date: Wed, 12 Sep 2007 12:08:45 +0200
>
> > Unfortunatly, there is no equivalent for this one.
> > This gives on my Opterons a nice "prefetchnta"
> >
> > prefetch(addr) is more like __builtin_prefetch(addr, 0, 3)
> >
> > I would like to avoid to zap L2 cache with useless data.
> >
> > __builtin_prefetch() is included from gcc 3.1 (2002), so every
> > platform should support it, as linux-2.6 requires gcc 3.2 at least.
> >
> > I guess you are going to tell me to first publish a patch to lkml :)
>
> Basically, yes :-) You won't be the only person to find this
> useful.
OK, let's try a normal prefetch(), I'll change it later when/if a
new generic macro is added. I added the missing 'static' and a comment
about the "struct {} dst_garbage". I also corrected spelling error on
patch title (collection)
Thank you
[PATCH] NET : convert IP route cache garbage collection from softirq processing
to a workqueue
When the periodic IP route cache flush is done (every 600 seconds on
default configuration), some hosts suffer a lot and eventually trigger
the "soft lockup" message.
dst_run_gc() is doing a scan of a possibly huge list of dst_entries,
eventually freeing some (less than 1%) of them, while holding the
dst_lock spinlock for the whole scan.
Then it rearms a timer to redo the full thing 1/10 s later...
The slowdown can last one minute or so, depending on how active are
the tcp sessions.
This second version of the patch converts the processing from a softirq
based one to a workqueue.
Even if the list of entries in garbage_list is huge, host is still
responsive to softirqs and can make progress.
Instead of resetting gc timer to 0.1 second if one entry was freed in a
gc run, we do this if more than 10% of entries were freed.
Before patch :
Aug 16 06:21:37 SRV1 kernel: BUG: soft lockup detected on CPU#0!
Aug 16 06:21:37 SRV1 kernel:
Aug 16 06:21:37 SRV1 kernel: Call Trace:
Aug 16 06:21:37 SRV1 kernel: <IRQ> [<ffffffff802286f0>]
wake_up_process+0x10/0x20
Aug 16 06:21:37 SRV1 kernel: [<ffffffff80251e09>] softlockup_tick+0xe9/0x110
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803cd380>] dst_run_gc+0x0/0x140
Aug 16 06:21:37 SRV1 kernel: [<ffffffff802376f3>] run_local_timers+0x13/0x20
Aug 16 06:21:37 SRV1 kernel: [<ffffffff802379c7>]
update_process_times+0x57/0x90
Aug 16 06:21:37 SRV1 kernel: [<ffffffff80216034>]
smp_local_timer_interrupt+0x34/0x60
Aug 16 06:21:37 SRV1 kernel: [<ffffffff802165cc>]
smp_apic_timer_interrupt+0x5c/0x80
Aug 16 06:21:37 SRV1 kernel: [<ffffffff8020a816>]
apic_timer_interrupt+0x66/0x70
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803cd3d3>] dst_run_gc+0x53/0x140
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803cd3c6>] dst_run_gc+0x46/0x140
Aug 16 06:21:37 SRV1 kernel: [<ffffffff80237148>] run_timer_softirq+0x148/0x1c0
Aug 16 06:21:37 SRV1 kernel: [<ffffffff8023340c>] __do_softirq+0x6c/0xe0
Aug 16 06:21:37 SRV1 kernel: [<ffffffff8020ad6c>] call_softirq+0x1c/0x30
Aug 16 06:21:37 SRV1 kernel: <EOI> [<ffffffff8020cb34>] do_softirq+0x34/0x90
Aug 16 06:21:37 SRV1 kernel: [<ffffffff802331cf>] local_bh_enable_ip+0x3f/0x60
Aug 16 06:21:37 SRV1 kernel: [<ffffffff80422913>] _spin_unlock_bh+0x13/0x20
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803dfde8>]
rt_garbage_collect+0x1d8/0x320
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803cd4dd>] dst_alloc+0x1d/0xa0
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803e1433>]
__ip_route_output_key+0x573/0x800
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803c02e2>] sock_common_recvmsg+0x32/0x50
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803e16dc>]
ip_route_output_flow+0x1c/0x60
Aug 16 06:21:37 SRV1 kernel: [<ffffffff80400160>] tcp_v4_connect+0x150/0x610
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803ebf07>]
inet_bind_bucket_create+0x17/0x60
Aug 16 06:21:37 SRV1 kernel: [<ffffffff8040cd16>]
inet_stream_connect+0xa6/0x2c0
Aug 16 06:21:37 SRV1 kernel: [<ffffffff80422981>] _spin_lock_bh+0x11/0x30
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803c0bdf>] lock_sock_nested+0xcf/0xe0
Aug 16 06:21:37 SRV1 kernel: [<ffffffff80422981>] _spin_lock_bh+0x11/0x30
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803be551>] sys_connect+0x71/0xa0
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803eee3f>] tcp_setsockopt+0x1f/0x30
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803c030f>]
sock_common_setsockopt+0xf/0x20
Aug 16 06:21:37 SRV1 kernel: [<ffffffff803be4bd>] sys_setsockopt+0x9d/0xc0
Aug 16 06:21:37 SRV1 kernel: [<ffffffff8028881e>] sys_ioctl+0x5e/0x80
Aug 16 06:21:37 SRV1 kernel: [<ffffffff80209c4e>] system_call+0x7e/0x83
After patch : (RT_CACHE_DEBUG set to 2 to get following traces)
dst_total: 75469 delayed: 74109 work_perf: 141 expires: 150 elapsed: 8092 us
dst_total: 78725 delayed: 73366 work_perf: 743 expires: 400 elapsed: 8542 us
dst_total: 86126 delayed: 71844 work_perf: 1522 expires: 775 elapsed: 8849 us
dst_total: 100173 delayed: 68791 work_perf: 3053 expires: 1256 elapsed: 9748 us
dst_total: 121798 delayed: 64711 work_perf: 4080 expires: 1997 elapsed: 10146 us
dst_total: 154522 delayed: 58316 work_perf: 6395 expires: 25 elapsed: 11402 us
dst_total: 154957 delayed: 58252 work_perf: 64 expires: 150 elapsed: 6148 us
dst_total: 157377 delayed: 57843 work_perf: 409 expires: 400 elapsed: 6350 us
dst_total: 163745 delayed: 56679 work_perf: 1164 expires: 775 elapsed: 7051 us
dst_total: 176577 delayed: 53965 work_perf: 2714 expires: 1389 elapsed: 8120 us
dst_total: 198993 delayed: 49627 work_perf: 4338 expires: 1997 elapsed: 8909 us
dst_total: 226638 delayed: 46865 work_perf: 2762 expires: 2748 elapsed: 7351 us
I successfully reduced the IP route cache of many hosts by a four factor
thanks to this patch. Previously, I had to disable "ip route flush cache"
to avoid crashes.
Signed-off-by: Eric Dumazet <[EMAIL PROTECTED]>
diff --git a/net/core/dst.c b/net/core/dst.c
index c6a0587..e250e01 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -9,6 +9,7 @@
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/kernel.h>
+#include <linux/workqueue.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/netdevice.h>
@@ -18,50 +19,72 @@
#include <net/dst.h>
-/* Locking strategy:
- * 1) Garbage collection state of dead destination cache
- * entries is protected by dst_lock.
- * 2) GC is run only from BH context, and is the only remover
- * of entries.
- * 3) Entries are added to the garbage list from both BH
- * and non-BH context, so local BH disabling is needed.
- * 4) All operations modify state, so a spinlock is used.
+/*
+ * Theory of operations:
+ * 1) We use a list, protected by a spinlock, to add
+ * new entries from both BH and non-BH context.
+ * 2) In order to keep spinlock held for a small delay,
+ * we use a second list where are stored long lived
+ * entries, that are handled by the garbage collect thread
+ * fired by a workqueue.
+ * 3) This list is guarded by a mutex,
+ * so that the gc_task and dst_dev_event() can be synchronized.
*/
-static struct dst_entry *dst_garbage_list;
#if RT_CACHE_DEBUG >= 2
static atomic_t dst_total = ATOMIC_INIT(0);
#endif
-static DEFINE_SPINLOCK(dst_lock);
-static unsigned long dst_gc_timer_expires;
-static unsigned long dst_gc_timer_inc = DST_GC_MAX;
-static void dst_run_gc(unsigned long);
+/*
+ * We want to keep lock & list close together
+ * to dirty as few cache lines as possible in __dst_free().
+ * As this is not a very strong hint, we dont force an alignment on SMP.
+ */
+static struct {
+ spinlock_t lock;
+ struct dst_entry *list;
+ unsigned long timer_inc;
+ unsigned long timer_expires;
+} dst_garbage = {
+ .lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
+ .timer_inc = DST_GC_MAX,
+};
+static void dst_gc_task(struct work_struct *work);
static void ___dst_free(struct dst_entry * dst);
-static DEFINE_TIMER(dst_gc_timer, dst_run_gc, DST_GC_MIN, 0);
+static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
-static void dst_run_gc(unsigned long dummy)
+static DEFINE_MUTEX(dst_gc_mutex);
+/*
+ * long lived entries are maintained in this list, guarded by dst_gc_mutex
+ */
+static struct dst_entry *dst_busy_list;
+
+static void dst_gc_task(struct work_struct *work)
{
int delayed = 0;
- int work_performed;
- struct dst_entry * dst, **dstp;
+ int work_performed = 0;
+ unsigned long expires = ~0L;
+ struct dst_entry *dst, *next, head;
+ struct dst_entry *last = &head;
+#if RT_CACHE_DEBUG >= 2
+ ktime_t time_start = ktime_get();
+ struct timespec elapsed;
+#endif
- if (!spin_trylock(&dst_lock)) {
- mod_timer(&dst_gc_timer, jiffies + HZ/10);
- return;
- }
+ mutex_lock(&dst_gc_mutex);
+ next = dst_busy_list;
- del_timer(&dst_gc_timer);
- dstp = &dst_garbage_list;
- work_performed = 0;
- while ((dst = *dstp) != NULL) {
- if (atomic_read(&dst->__refcnt)) {
- dstp = &dst->next;
+loop:
+ while ((dst = next) != NULL) {
+ next = dst->next;
+ prefetch(&next->next);
+ if (likely(atomic_read(&dst->__refcnt))) {
+ last->next = dst;
+ last = dst;
delayed++;
continue;
}
- *dstp = dst->next;
- work_performed = 1;
+ work_performed++;
dst = dst_destroy(dst);
if (dst) {
@@ -77,38 +100,56 @@ static void dst_run_gc(unsigned long dummy)
continue;
___dst_free(dst);
- dst->next = *dstp;
- *dstp = dst;
- dstp = &dst->next;
+ dst->next = next;
+ next = dst;
}
}
- if (!dst_garbage_list) {
- dst_gc_timer_inc = DST_GC_MAX;
- goto out;
+
+ spin_lock_bh(&dst_garbage.lock);
+ next = dst_garbage.list;
+ if (next) {
+ dst_garbage.list = NULL;
+ spin_unlock_bh(&dst_garbage.lock);
+ goto loop;
}
- if (!work_performed) {
- if ((dst_gc_timer_expires += dst_gc_timer_inc) > DST_GC_MAX)
- dst_gc_timer_expires = DST_GC_MAX;
- dst_gc_timer_inc += DST_GC_INC;
- } else {
- dst_gc_timer_inc = DST_GC_INC;
- dst_gc_timer_expires = DST_GC_MIN;
+ last->next = NULL;
+ dst_busy_list = head.next;
+ if (!dst_busy_list)
+ dst_garbage.timer_inc = DST_GC_MAX;
+ else {
+ /*
+ * if we freed less than 1/10 of delayed entries,
+ * we can sleep longer.
+ */
+ if (work_performed <= delayed/10) {
+ dst_garbage.timer_expires += dst_garbage.timer_inc;
+ if (dst_garbage.timer_expires > DST_GC_MAX)
+ dst_garbage.timer_expires = DST_GC_MAX;
+ dst_garbage.timer_inc += DST_GC_INC;
+ } else {
+ dst_garbage.timer_inc = DST_GC_INC;
+ dst_garbage.timer_expires = DST_GC_MIN;
+ }
+ expires = dst_garbage.timer_expires;
+ /*
+ * if the next desired timer is more than 4 seconds in the
future
+ * then round the timer to whole seconds
+ */
+ if (expires > 4*HZ)
+ expires = round_jiffies_relative(expires);
+ schedule_delayed_work(&dst_gc_work, expires);
}
+
+ spin_unlock_bh(&dst_garbage.lock);
+ mutex_unlock(&dst_gc_mutex);
#if RT_CACHE_DEBUG >= 2
- printk("dst_total: %d/%d %ld\n",
- atomic_read(&dst_total), delayed, dst_gc_timer_expires);
+ elapsed = ktime_to_timespec(ktime_sub(ktime_get(), time_start));
+ printk(KERN_DEBUG "dst_total: %d delayed: %d work_perf: %d"
+ " expires: %lu elapsed: %lu us\n",
+ atomic_read(&dst_total), delayed, work_performed,
+ expires,
+ elapsed.tv_sec * USEC_PER_SEC + elapsed.tv_nsec /
NSEC_PER_USEC);
#endif
- /* if the next desired timer is more than 4 seconds in the future
- * then round the timer to whole seconds
- */
- if (dst_gc_timer_expires > 4*HZ)
- mod_timer(&dst_gc_timer,
- round_jiffies(jiffies + dst_gc_timer_expires));
- else
- mod_timer(&dst_gc_timer, jiffies + dst_gc_timer_expires);
-
-out:
- spin_unlock(&dst_lock);
}
static int dst_discard(struct sk_buff *skb)
@@ -153,16 +194,16 @@ static void ___dst_free(struct dst_entry * dst)
void __dst_free(struct dst_entry * dst)
{
- spin_lock_bh(&dst_lock);
+ spin_lock_bh(&dst_garbage.lock);
___dst_free(dst);
- dst->next = dst_garbage_list;
- dst_garbage_list = dst;
- if (dst_gc_timer_inc > DST_GC_INC) {
- dst_gc_timer_inc = DST_GC_INC;
- dst_gc_timer_expires = DST_GC_MIN;
- mod_timer(&dst_gc_timer, jiffies + dst_gc_timer_expires);
+ dst->next = dst_garbage.list;
+ dst_garbage.list = dst;
+ if (dst_garbage.timer_inc > DST_GC_INC) {
+ dst_garbage.timer_inc = DST_GC_INC;
+ dst_garbage.timer_expires = DST_GC_MIN;
+ schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
}
- spin_unlock_bh(&dst_lock);
+ spin_unlock_bh(&dst_garbage.lock);
}
struct dst_entry *dst_destroy(struct dst_entry * dst)
@@ -250,16 +291,30 @@ static inline void dst_ifdown(struct dst_entry *dst,
struct net_device *dev,
static int dst_dev_event(struct notifier_block *this, unsigned long event,
void *ptr)
{
struct net_device *dev = ptr;
- struct dst_entry *dst;
+ struct dst_entry *dst, *last = NULL;
switch (event) {
case NETDEV_UNREGISTER:
case NETDEV_DOWN:
- spin_lock_bh(&dst_lock);
- for (dst = dst_garbage_list; dst; dst = dst->next) {
+ mutex_lock(&dst_gc_mutex);
+ for (dst = dst_busy_list; dst; dst = dst->next) {
+ last = dst;
+ dst_ifdown(dst, dev, event != NETDEV_DOWN);
+ }
+
+ spin_lock_bh(&dst_garbage.lock);
+ dst = dst_garbage.list;
+ dst_garbage.list = NULL;
+ spin_unlock_bh(&dst_garbage.lock);
+
+ if (last)
+ last->next = dst;
+ else
+ dst_busy_list = dst;
+ for (; dst; dst = dst->next) {
dst_ifdown(dst, dev, event != NETDEV_DOWN);
}
- spin_unlock_bh(&dst_lock);
+ mutex_unlock(&dst_gc_mutex);
break;
}
return NOTIFY_DONE;
-
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