Re: [patch 2/4] net: percpufy frequently used vars -- struct proto.memory_allocated

From: Ravikiran G Thirumalai
Date: Wed Mar 08 2006 - 15:50:56 EST

On Tue, Mar 07, 2006 at 07:22:34PM -0800, Andrew Morton wrote:
> Ravikiran G Thirumalai <kiran@xxxxxxxxxxxx> wrote:
> >
> > The problem is percpu_counter_sum has to read all the cpus cachelines. If
> > we have to use percpu_counter_sum everywhere, then might as well use plain
> > per-cpu counters instead of batching ones no?
>
> I didn't say "use it everywhere" ;)

:) No you did not. Sorry. When the counter shows large varience it will affect
all places where it is read and it wasn't clear to me where to use
percpu_counter_sum vs percpu_counter_read in the context of the patch.
But yes, using percpu_counter_sum at the critical points makes things better.
Thanks for pointing it out. Here is an attempt on those lines.

>
> > Maybe, on very large cpu counts,
> > we should just change the FBC_BATCH so that variance does not go quadratic.
> > Something like 32. So that variance is 32 * NR_CPUS in that case, instead
> > of (NR_CPUS * NR_CPUS * 2) currently. Comments?
>
> Sure, we need to make that happen. But it got all mixed up with the
> spinlock removal and it does need quite some thought and testing and
> documentation to help developers to choose the right settings and
> appropriate selection of defaults, etc.

I was thinking on the lines of something like the following as a simple fix
to the quadratic variance. But yes, it needs some experimentation before hand..

#if NR_CPUS >= 16
#define FBC_BATCH (32)
#else
#define FBC_BATCH (NR_CPUS*4)
#endif

Thanks,
Kiran


Change struct proto->memory_allocated to a batching per-CPU counter
(percpu_counter) from an atomic_t. A batching counter is better than a
plain per-CPU counter as this field is read often.

Changes since last post: Use the more accurate percpu_counter_sum() at
critical places.

Signed-off-by: Pravin B. Shelar <pravins@xxxxxxxxxxxxxx>
Signed-off-by: Ravikiran Thirumalai <kiran@xxxxxxxxxxxx>
Signed-off-by: Shai Fultheim <shai@xxxxxxxxxxxx>

Index: linux-2.6.16-rc5mm3/include/net/sock.h
===================================================================
--- linux-2.6.16-rc5mm3.orig/include/net/sock.h 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/include/net/sock.h 2006-03-08 11:03:19.000000000 -0800
@@ -48,6 +48,7 @@
#include <linux/netdevice.h>
#include <linux/skbuff.h> /* struct sk_buff */
#include <linux/security.h>
+#include <linux/percpu_counter.h>

#include <linux/filter.h>

@@ -541,8 +542,9 @@ struct proto {

/* Memory pressure */
void (*enter_memory_pressure)(void);
- atomic_t *memory_allocated; /* Current allocated memory. */
+ struct percpu_counter *memory_allocated; /* Current allocated memory. */
atomic_t *sockets_allocated; /* Current number of sockets. */
+
/*
* Pressure flag: try to collapse.
* Technical note: it is used by multiple contexts non atomically.
Index: linux-2.6.16-rc5mm3/include/net/tcp.h
===================================================================
--- linux-2.6.16-rc5mm3.orig/include/net/tcp.h 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/include/net/tcp.h 2006-03-08 11:03:19.000000000 -0800
@@ -225,7 +225,7 @@ extern int sysctl_tcp_abc;
extern int sysctl_tcp_mtu_probing;
extern int sysctl_tcp_base_mss;

-extern atomic_t tcp_memory_allocated;
+extern struct percpu_counter tcp_memory_allocated;
extern atomic_t tcp_sockets_allocated;
extern int tcp_memory_pressure;

Index: linux-2.6.16-rc5mm3/net/core/sock.c
===================================================================
--- linux-2.6.16-rc5mm3.orig/net/core/sock.c 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/net/core/sock.c 2006-03-08 11:03:19.000000000 -0800
@@ -1616,12 +1616,13 @@ static char proto_method_implemented(con

static void proto_seq_printf(struct seq_file *seq, struct proto *proto)
{
- seq_printf(seq, "%-9s %4u %6d %6d %-3s %6u %-3s %-10s "
+ seq_printf(seq, "%-9s %4u %6d %6lu %-3s %6u %-3s %-10s "
"%2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c\n",
proto->name,
proto->obj_size,
proto->sockets_allocated != NULL ? atomic_read(proto->sockets_allocated) : -1,
- proto->memory_allocated != NULL ? atomic_read(proto->memory_allocated) : -1,
+ proto->memory_allocated != NULL ?
+ percpu_counter_read_positive(proto->memory_allocated) : -1,
proto->memory_pressure != NULL ? *proto->memory_pressure ? "yes" : "no" : "NI",
proto->max_header,
proto->slab == NULL ? "no" : "yes",
Index: linux-2.6.16-rc5mm3/net/core/stream.c
===================================================================
--- linux-2.6.16-rc5mm3.orig/net/core/stream.c 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/net/core/stream.c 2006-03-08 11:08:28.000000000 -0800
@@ -196,11 +196,11 @@ EXPORT_SYMBOL(sk_stream_error);
void __sk_stream_mem_reclaim(struct sock *sk)
{
if (sk->sk_forward_alloc >= SK_STREAM_MEM_QUANTUM) {
- atomic_sub(sk->sk_forward_alloc / SK_STREAM_MEM_QUANTUM,
- sk->sk_prot->memory_allocated);
+ percpu_counter_mod_bh(sk->sk_prot->memory_allocated,
+ -(sk->sk_forward_alloc / SK_STREAM_MEM_QUANTUM));
sk->sk_forward_alloc &= SK_STREAM_MEM_QUANTUM - 1;
if (*sk->sk_prot->memory_pressure &&
- (atomic_read(sk->sk_prot->memory_allocated) <
+ (percpu_counter_read(sk->sk_prot->memory_allocated) <
sk->sk_prot->sysctl_mem[0]))
*sk->sk_prot->memory_pressure = 0;
}
@@ -213,23 +213,26 @@ int sk_stream_mem_schedule(struct sock *
int amt = sk_stream_pages(size);

sk->sk_forward_alloc += amt * SK_STREAM_MEM_QUANTUM;
- atomic_add(amt, sk->sk_prot->memory_allocated);
+ percpu_counter_mod_bh(sk->sk_prot->memory_allocated, amt);

/* Under limit. */
- if (atomic_read(sk->sk_prot->memory_allocated) < sk->sk_prot->sysctl_mem[0]) {
+ if (percpu_counter_read(sk->sk_prot->memory_allocated) <
+ sk->sk_prot->sysctl_mem[0]) {
if (*sk->sk_prot->memory_pressure)
*sk->sk_prot->memory_pressure = 0;
return 1;
}

/* Over hard limit. */
- if (atomic_read(sk->sk_prot->memory_allocated) > sk->sk_prot->sysctl_mem[2]) {
+ if (percpu_counter_sum(sk->sk_prot->memory_allocated) >
+ sk->sk_prot->sysctl_mem[2]) {
sk->sk_prot->enter_memory_pressure();
goto suppress_allocation;
}

/* Under pressure. */
- if (atomic_read(sk->sk_prot->memory_allocated) > sk->sk_prot->sysctl_mem[1])
+ if (percpu_counter_read(sk->sk_prot->memory_allocated) >
+ sk->sk_prot->sysctl_mem[1])
sk->sk_prot->enter_memory_pressure();

if (kind) {
@@ -259,7 +262,7 @@ suppress_allocation:

/* Alas. Undo changes. */
sk->sk_forward_alloc -= amt * SK_STREAM_MEM_QUANTUM;
- atomic_sub(amt, sk->sk_prot->memory_allocated);
+ percpu_counter_mod_bh(sk->sk_prot->memory_allocated, -amt);
return 0;
}

Index: linux-2.6.16-rc5mm3/net/decnet/af_decnet.c
===================================================================
--- linux-2.6.16-rc5mm3.orig/net/decnet/af_decnet.c 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/net/decnet/af_decnet.c 2006-03-08 11:03:19.000000000 -0800
@@ -154,7 +154,7 @@ static const struct proto_ops dn_proto_o
static DEFINE_RWLOCK(dn_hash_lock);
static struct hlist_head dn_sk_hash[DN_SK_HASH_SIZE];
static struct hlist_head dn_wild_sk;
-static atomic_t decnet_memory_allocated;
+static struct percpu_counter decnet_memory_allocated;

static int __dn_setsockopt(struct socket *sock, int level, int optname, char __user *optval, int optlen, int flags);
static int __dn_getsockopt(struct socket *sock, int level, int optname, char __user *optval, int __user *optlen, int flags);
@@ -2383,7 +2383,8 @@ static int __init decnet_init(void)
rc = proto_register(&dn_proto, 1);
if (rc != 0)
goto out;
-
+
+ percpu_counter_init(&decnet_memory_allocated);
dn_neigh_init();
dn_dev_init();
dn_route_init();
@@ -2424,6 +2425,7 @@ static void __exit decnet_exit(void)
proc_net_remove("decnet");

proto_unregister(&dn_proto);
+ percpu_counter_destroy(&decnet_memory_allocated);
}
module_exit(decnet_exit);
#endif
Index: linux-2.6.16-rc5mm3/net/ipv4/proc.c
===================================================================
--- linux-2.6.16-rc5mm3.orig/net/ipv4/proc.c 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/net/ipv4/proc.c 2006-03-08 11:03:19.000000000 -0800
@@ -61,10 +61,10 @@ static int fold_prot_inuse(struct proto
static int sockstat_seq_show(struct seq_file *seq, void *v)
{
socket_seq_show(seq);
- seq_printf(seq, "TCP: inuse %d orphan %d tw %d alloc %d mem %d\n",
+ seq_printf(seq, "TCP: inuse %d orphan %d tw %d alloc %d mem %lu\n",
fold_prot_inuse(&tcp_prot), atomic_read(&tcp_orphan_count),
tcp_death_row.tw_count, atomic_read(&tcp_sockets_allocated),
- atomic_read(&tcp_memory_allocated));
+ percpu_counter_read_positive(&tcp_memory_allocated));
seq_printf(seq, "UDP: inuse %d\n", fold_prot_inuse(&udp_prot));
seq_printf(seq, "RAW: inuse %d\n", fold_prot_inuse(&raw_prot));
seq_printf(seq, "FRAG: inuse %d memory %d\n", ip_frag_nqueues,
Index: linux-2.6.16-rc5mm3/net/ipv4/tcp.c
===================================================================
--- linux-2.6.16-rc5mm3.orig/net/ipv4/tcp.c 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/net/ipv4/tcp.c 2006-03-08 11:16:33.000000000 -0800
@@ -283,7 +283,7 @@ EXPORT_SYMBOL(sysctl_tcp_mem);
EXPORT_SYMBOL(sysctl_tcp_rmem);
EXPORT_SYMBOL(sysctl_tcp_wmem);

-atomic_t tcp_memory_allocated; /* Current allocated memory. */
+struct percpu_counter tcp_memory_allocated; /* Current allocated memory. */
atomic_t tcp_sockets_allocated; /* Current number of TCP sockets. */

EXPORT_SYMBOL(tcp_memory_allocated);
@@ -1593,7 +1593,7 @@ adjudge_to_death:
sk_stream_mem_reclaim(sk);
if (atomic_read(sk->sk_prot->orphan_count) > sysctl_tcp_max_orphans ||
(sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
- atomic_read(&tcp_memory_allocated) > sysctl_tcp_mem[2])) {
+ percpu_counter_sum(&tcp_memory_allocated) > sysctl_tcp_mem[2])) {
if (net_ratelimit())
printk(KERN_INFO "TCP: too many of orphaned "
"sockets\n");
@@ -2127,6 +2127,8 @@ void __init tcp_init(void)
"(established %d bind %d)\n",
tcp_hashinfo.ehash_size << 1, tcp_hashinfo.bhash_size);

+ percpu_counter_init(&tcp_memory_allocated);
+
tcp_register_congestion_control(&tcp_reno);
}

Index: linux-2.6.16-rc5mm3/net/ipv4/tcp_input.c
===================================================================
--- linux-2.6.16-rc5mm3.orig/net/ipv4/tcp_input.c 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/net/ipv4/tcp_input.c 2006-03-08 11:03:19.000000000 -0800
@@ -333,7 +333,7 @@ static void tcp_clamp_window(struct sock
if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
!(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
!tcp_memory_pressure &&
- atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
+ percpu_counter_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
sysctl_tcp_rmem[2]);
}
@@ -3555,7 +3555,7 @@ static int tcp_should_expand_sndbuf(stru
return 0;

/* If we are under soft global TCP memory pressure, do not expand. */
- if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
+ if (percpu_counter_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
return 0;

/* If we filled the congestion window, do not expand. */
Index: linux-2.6.16-rc5mm3/net/ipv4/tcp_timer.c
===================================================================
--- linux-2.6.16-rc5mm3.orig/net/ipv4/tcp_timer.c 2006-03-08 10:36:07.000000000 -0800
+++ linux-2.6.16-rc5mm3/net/ipv4/tcp_timer.c 2006-03-08 11:39:05.000000000 -0800
@@ -80,7 +80,7 @@ static int tcp_out_of_resources(struct s

if (orphans >= sysctl_tcp_max_orphans ||
(sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
- atomic_read(&tcp_memory_allocated) > sysctl_tcp_mem[2])) {
+ percpu_counter_sum(&tcp_memory_allocated) > sysctl_tcp_mem[2])) {
if (net_ratelimit())
printk(KERN_INFO "Out of socket memory\n");

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/