snmp: reduce percpu needs by 50%
Eric Dumazet [Fri, 10 Jun 2011 19:45:51 +0000 (19:45 +0000)]
SNMP mibs use two percpu arrays, one used in BH context, another in USER
context. With increasing number of cpus in machines, and fact that ipv6
uses per network device ipstats_mib, this is consuming a lot of memory
if many network devices are registered.

commit be281e554e2a (ipv6: reduce per device ICMP mib sizes) shrinked
percpu needs for ipv6, but we can reduce memory use a bit more.

With recent percpu infrastructure (irqsafe_cpu_inc() ...), we no longer
need this BH/USER separation since we can update counters in a single
x86 instruction, regardless of the BH/USER context.

Other arches than x86 might need to disable irq in their
irqsafe_cpu_inc() implementation : If this happens to be a problem, we
can make SNMP_ARRAY_SZ arch dependent, but a previous poll
( https://lkml.org/lkml/2011/3/17/174 ) to arch maintainers did not
raise strong opposition.

Only on 32bit arches, we need to disable BH for 64bit counters updates
done from USER context (currently used for IP MIB)

This also reduces vmlinux size :

1) x86_64 build
$ size vmlinux.before vmlinux.after
   text    data     bss     dec     hex filename
7853650 1293772 1896448 11043870  a8841e vmlinux.before
7850578 1293772 1896448 11040798  a8781e vmlinux.after

2) i386  build
$ size vmlinux.before vmlinux.afterpatch
   text    data     bss     dec     hex filename
6039335  635076 3670016 10344427  9dd7eb vmlinux.before
6037342  635076 3670016 10342434  9dd022 vmlinux.afterpatch

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Andi Kleen <andi@firstfloor.org>
CC: Ingo Molnar <mingo@elte.hu>
CC: Tejun Heo <tj@kernel.org>
CC: Christoph Lameter <cl@linux-foundation.org>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org
CC: linux-arch@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/snmp.h
net/ipv4/af_inet.c

index 479083a..8f0f9ac 100644 (file)
@@ -116,57 +116,51 @@ struct linux_xfrm_mib {
        unsigned long   mibs[LINUX_MIB_XFRMMAX];
 };
 
-/* 
- * FIXME: On x86 and some other CPUs the split into user and softirq parts
- * is not needed because addl $1,memory is atomic against interrupts (but 
- * atomic_inc would be overkill because of the lock cycles). Wants new 
- * nonlocked_atomic_inc() primitives -AK
- */ 
+#define SNMP_ARRAY_SZ 1
+
 #define DEFINE_SNMP_STAT(type, name)   \
-       __typeof__(type) __percpu *name[2]
+       __typeof__(type) __percpu *name[SNMP_ARRAY_SZ]
 #define DEFINE_SNMP_STAT_ATOMIC(type, name)    \
        __typeof__(type) *name
 #define DECLARE_SNMP_STAT(type, name)  \
-       extern __typeof__(type) __percpu *name[2]
-
-#define SNMP_STAT_BHPTR(name)  (name[0])
-#define SNMP_STAT_USRPTR(name) (name[1])
+       extern __typeof__(type) __percpu *name[SNMP_ARRAY_SZ]
 
 #define SNMP_INC_STATS_BH(mib, field)  \
                        __this_cpu_inc(mib[0]->mibs[field])
+
 #define SNMP_INC_STATS_USER(mib, field)        \
-                       this_cpu_inc(mib[1]->mibs[field])
+                       irqsafe_cpu_inc(mib[0]->mibs[field])
+
 #define SNMP_INC_STATS_ATOMIC_LONG(mib, field) \
                        atomic_long_inc(&mib->mibs[field])
+
 #define SNMP_INC_STATS(mib, field)     \
-                       this_cpu_inc(mib[!in_softirq()]->mibs[field])
+                       irqsafe_cpu_inc(mib[0]->mibs[field])
+
 #define SNMP_DEC_STATS(mib, field)     \
-                       this_cpu_dec(mib[!in_softirq()]->mibs[field])
+                       irqsafe_cpu_dec(mib[0]->mibs[field])
+
 #define SNMP_ADD_STATS_BH(mib, field, addend)  \
                        __this_cpu_add(mib[0]->mibs[field], addend)
+
 #define SNMP_ADD_STATS_USER(mib, field, addend)        \
-                       this_cpu_add(mib[1]->mibs[field], addend)
+                       irqsafe_cpu_add(mib[0]->mibs[field], addend)
+
 #define SNMP_ADD_STATS(mib, field, addend)     \
-                       this_cpu_add(mib[!in_softirq()]->mibs[field], addend)
+                       irqsafe_cpu_add(mib[0]->mibs[field], addend)
 /*
  * Use "__typeof__(*mib[0]) *ptr" instead of "__typeof__(mib[0]) ptr"
  * to make @ptr a non-percpu pointer.
  */
 #define SNMP_UPD_PO_STATS(mib, basefield, addend)      \
        do { \
-               __typeof__(*mib[0]) *ptr; \
-               preempt_disable(); \
-               ptr = this_cpu_ptr((mib)[!in_softirq()]); \
-               ptr->mibs[basefield##PKTS]++; \
-               ptr->mibs[basefield##OCTETS] += addend;\
-               preempt_enable(); \
+               irqsafe_cpu_inc(mib[0]->mibs[basefield##PKTS]);         \
+               irqsafe_cpu_add(mib[0]->mibs[basefield##OCTETS], addend);       \
        } while (0)
 #define SNMP_UPD_PO_STATS_BH(mib, basefield, addend)   \
        do { \
-               __typeof__(*mib[0]) *ptr = \
-                       __this_cpu_ptr((mib)[0]); \
-               ptr->mibs[basefield##PKTS]++; \
-               ptr->mibs[basefield##OCTETS] += addend;\
+               __this_cpu_inc(mib[0]->mibs[basefield##PKTS]);          \
+               __this_cpu_add(mib[0]->mibs[basefield##OCTETS], addend);        \
        } while (0)
 
 
@@ -179,40 +173,20 @@ struct linux_xfrm_mib {
                ptr->mibs[field] += addend;                             \
                u64_stats_update_end(&ptr->syncp);                      \
        } while (0)
+
 #define SNMP_ADD_STATS64_USER(mib, field, addend)                      \
        do {                                                            \
-               __typeof__(*mib[0]) *ptr;                               \
-               preempt_disable();                                      \
-               ptr = __this_cpu_ptr((mib)[1]);                         \
-               u64_stats_update_begin(&ptr->syncp);                    \
-               ptr->mibs[field] += addend;                             \
-               u64_stats_update_end(&ptr->syncp);                      \
-               preempt_enable();                                       \
+               local_bh_disable();                                     \
+               SNMP_ADD_STATS64_BH(mib, field, addend);                \
+               local_bh_enable();                                      \
        } while (0)
+
 #define SNMP_ADD_STATS64(mib, field, addend)                           \
-       do {                                                            \
-               __typeof__(*mib[0]) *ptr;                               \
-               preempt_disable();                                      \
-               ptr = __this_cpu_ptr((mib)[!in_softirq()]);             \
-               u64_stats_update_begin(&ptr->syncp);                    \
-               ptr->mibs[field] += addend;                             \
-               u64_stats_update_end(&ptr->syncp);                      \
-               preempt_enable();                                       \
-       } while (0)
+               SNMP_ADD_STATS64_USER(mib, field, addend)
+
 #define SNMP_INC_STATS64_BH(mib, field) SNMP_ADD_STATS64_BH(mib, field, 1)
 #define SNMP_INC_STATS64_USER(mib, field) SNMP_ADD_STATS64_USER(mib, field, 1)
 #define SNMP_INC_STATS64(mib, field) SNMP_ADD_STATS64(mib, field, 1)
-#define SNMP_UPD_PO_STATS64(mib, basefield, addend)                    \
-       do {                                                            \
-               __typeof__(*mib[0]) *ptr;                               \
-               preempt_disable();                                      \
-               ptr = __this_cpu_ptr((mib)[!in_softirq()]);             \
-               u64_stats_update_begin(&ptr->syncp);                    \
-               ptr->mibs[basefield##PKTS]++;                           \
-               ptr->mibs[basefield##OCTETS] += addend;                 \
-               u64_stats_update_end(&ptr->syncp);                      \
-               preempt_enable();                                       \
-       } while (0)
 #define SNMP_UPD_PO_STATS64_BH(mib, basefield, addend)                 \
        do {                                                            \
                __typeof__(*mib[0]) *ptr;                               \
@@ -222,6 +196,12 @@ struct linux_xfrm_mib {
                ptr->mibs[basefield##OCTETS] += addend;                 \
                u64_stats_update_end(&ptr->syncp);                      \
        } while (0)
+#define SNMP_UPD_PO_STATS64(mib, basefield, addend)                    \
+       do {                                                            \
+               local_bh_disable();                                     \
+               SNMP_UPD_PO_STATS64_BH(mib, basefield, addend);         \
+               local_bh_enable();                                      \
+       } while (0)
 #else
 #define SNMP_INC_STATS64_BH(mib, field)                SNMP_INC_STATS_BH(mib, field)
 #define SNMP_INC_STATS64_USER(mib, field)      SNMP_INC_STATS_USER(mib, field)
index 9c19260..83673d2 100644 (file)
@@ -1437,11 +1437,11 @@ EXPORT_SYMBOL_GPL(inet_ctl_sock_create);
 unsigned long snmp_fold_field(void __percpu *mib[], int offt)
 {
        unsigned long res = 0;
-       int i;
+       int i, j;
 
        for_each_possible_cpu(i) {
-               res += *(((unsigned long *) per_cpu_ptr(mib[0], i)) + offt);
-               res += *(((unsigned long *) per_cpu_ptr(mib[1], i)) + offt);
+               for (j = 0; j < SNMP_ARRAY_SZ; j++)
+                       res += *(((unsigned long *) per_cpu_ptr(mib[j], i)) + offt);
        }
        return res;
 }
@@ -1455,28 +1455,19 @@ u64 snmp_fold_field64(void __percpu *mib[], int offt, size_t syncp_offset)
        int cpu;
 
        for_each_possible_cpu(cpu) {
-               void *bhptr, *userptr;
+               void *bhptr;
                struct u64_stats_sync *syncp;
-               u64 v_bh, v_user;
+               u64 v;
                unsigned int start;
 
-               /* first mib used by softirq context, we must use _bh() accessors */
-               bhptr = per_cpu_ptr(SNMP_STAT_BHPTR(mib), cpu);
+               bhptr = per_cpu_ptr(mib[0], cpu);
                syncp = (struct u64_stats_sync *)(bhptr + syncp_offset);
                do {
                        start = u64_stats_fetch_begin_bh(syncp);
-                       v_bh = *(((u64 *) bhptr) + offt);
+                       v = *(((u64 *) bhptr) + offt);
                } while (u64_stats_fetch_retry_bh(syncp, start));
 
-               /* second mib used in USER context */
-               userptr = per_cpu_ptr(SNMP_STAT_USRPTR(mib), cpu);
-               syncp = (struct u64_stats_sync *)(userptr + syncp_offset);
-               do {
-                       start = u64_stats_fetch_begin(syncp);
-                       v_user = *(((u64 *) userptr) + offt);
-               } while (u64_stats_fetch_retry(syncp, start));
-
-               res += v_bh + v_user;
+               res += v;
        }
        return res;
 }
@@ -1488,25 +1479,28 @@ int snmp_mib_init(void __percpu *ptr[2], size_t mibsize, size_t align)
        BUG_ON(ptr == NULL);
        ptr[0] = __alloc_percpu(mibsize, align);
        if (!ptr[0])
-               goto err0;
+               return -ENOMEM;
+#if SNMP_ARRAY_SZ == 2
        ptr[1] = __alloc_percpu(mibsize, align);
-       if (!ptr[1])
-               goto err1;
+       if (!ptr[1]) {
+               free_percpu(ptr[0]);
+               ptr[0] = NULL;
+               return -ENOMEM;
+       }
+#endif
        return 0;
-err1:
-       free_percpu(ptr[0]);
-       ptr[0] = NULL;
-err0:
-       return -ENOMEM;
 }
 EXPORT_SYMBOL_GPL(snmp_mib_init);
 
-void snmp_mib_free(void __percpu *ptr[2])
+void snmp_mib_free(void __percpu *ptr[SNMP_ARRAY_SZ])
 {
+       int i;
+
        BUG_ON(ptr == NULL);
-       free_percpu(ptr[0]);
-       free_percpu(ptr[1]);
-       ptr[0] = ptr[1] = NULL;
+       for (i = 0; i < SNMP_ARRAY_SZ; i++) {
+               free_percpu(ptr[i]);
+               ptr[i] = NULL;
+       }
 }
 EXPORT_SYMBOL_GPL(snmp_mib_free);