#regzbot ^introduced 10befea91b61c4e2c2d1df06a2e978d182fcf792
We are making heavy use of mqueues, and noticed a degradation of performance between 4.18 & 5.10 linux kernels.
After a gross per-version tracing, we did kernel bisection between 5.8 and 5.9
and traced the issue to a 10 patches (of which 9 where skipped as they didn't boot) between:
commit 10befea91b61c4e2c2d1df06a2e978d182fcf792 (HEAD, refs/bisect/bad)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:27 2020 -0700
mm: memcg/slab: use a single set of kmem_caches for all allocations
and:
commit 286e04b8ed7a04279ae277f0f024430246ea5eec (refs/bisect/good-286e04b8ed7a04279ae277f0f024430246ea5eec)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:20:52 2020 -0700
mm: memcg/slab: allocate obj_cgroups for non-root slab pages
All of them are part of the "The new cgroup slab memory controller" patchset:
https://lore.kernel.org/all/20200623174037.3951353-18-guro@xxxxxx/T/
from Roman Gushchin, which moves the accounting for page level to the object level.
Measurements where done using the a test programmtest, which measures mix/average/max time mqueue_send/mqueue_rcv,
and average for getppid, both measured over 100 000 runs. Results are shown in the following table
+----------+--------------------------+-------------------------+----------------+
| kernel | mqueue_rcv (ns) | mqueue_send (ns) | getppid |
| version | min avg max variation | min avg max variation | (ns) variation |
+----------+--------------------------+-------------------------+----------------+
| 4.18.45 | 351 382 17533 base | 383 410 13178 base | 149 base |
| 5.8-good | 380 392 7156 -2,55% | 376 384 6225 6,77% | 169 -11,83% |
| 5.8-bad | 524 530 5310 -27,92% | 512 519 8775 -21,00% | 169 -11,83% |
| 5.10 | 520 533 4078 -28,33% | 518 534 8108 -23,22% | 167 -10,78% |
| 5.15 | 431 444 8440 -13,96% | 425 437 6170 -6,18% | 171 -12,87% |
| 6.03 | 474 614 3881 -37,79% | 482 693 931 -40,84% | 171 -12,87% |
+----------+--------------------------+-------------------------+-----------------
Below you will find the following appendices:
- raw GOOD bisect results
- raw BAD bisect results
- test code source code
- bisect results
Friendly,
Sven Luther
GOOD bisect results:
====================
# uname -a
Linux axxiax86-64 5.8.0-5-286e04b8ed7a04279ae277f0f024430246ea5eec-good #1 SMP PREEMPT Fri Jul 29 11:01:19 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
# ./mqtest
RX: 380/392/7156
TX: 376/384/6225
Accumulated time for 100000 getppid, 16924653ns
Average time per getppid: 169ns
# ./mqtest
RX: 383/397/6300
TX: 377/385/8258
Accumulated time for 100000 getppid, 16915580ns
Average time per getppid: 169ns
# ./mqtest
RX: 385/397/7690
TX: 377/385/4244
Accumulated time for 100000 getppid, 16922910ns
Average time per getppid: 169ns
BAD bisect results:
===================
# uname -a
Linux axxiax86-64 5.8.0-5-10befea91b61c4e2c2d1df06a2e978d182fcf792-bad #1 SMP PREEMPT Fri Jul 29 11:01:19 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
# ./mqtest
RX: 524/530/5310
TX: 512/519/8775
Accumulated time for 100000 getppid, 16921865ns
Average time per getppid: 169ns
# ./mqtest
RX: 520/525/8204
TX: 514/522/7420
Accumulated time for 100000 getppid, 16931493ns
Average time per getppid: 169ns
# ./mqtest
RX: 520/525/8128
TX: 512/519/5340
Accumulated time for 100000 getppid, 16921535ns
Average time per getppid: 169ns
Test programm:
==============
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <time.h>
#include <mqueue.h>
struct sysc_meas {
int64_t min;
int64_t max;
int64_t sum;
int64_t count;
};
static inline uint64_t __cputime_get(void)
{
unsigned long l, h;
asm volatile("rdtsc" : "=a" (l), "=d" (h));
return ((uint64_t) h << 32) | l;
}
static inline int64_t __cputime_ns(uint64_t cputime)
{
/* Note, it is assumed thatTSC clock is 2.2G */
return (cputime * 5) / 11;
}
static inline uint64_t __cputime_get_ns()
{
return __cputime_ns(__cputime_get());
}
static void sysc_meas_init(struct sysc_meas *sm)
{
sm->min = INT64_MAX;
sm->max = INT64_MIN;
sm->sum = sm->count = 0;
}
static void sysc_meas_add(struct sysc_meas *sm, int64_t value)
{
if (value > sm->max)
sm->max = value;
if (value < sm->min)
sm->min = value;
sm->sum += value;
sm->count++;
}
static void sysc_mq(uint32_t count)
{
int fd;
struct mq_attr mq_attr;
uint64_t ts;
struct sysc_meas sm_tx, sm_rx;
char dummy[256];
if (!count)
return;
mq_unlink("/sysc_mq");
memset(&mq_attr, 0, sizeof(mq_attr));
mq_attr.mq_maxmsg = 10;
mq_attr.mq_msgsize =
sizeof(dummy);
fd = mq_open("/sysc_mq", O_RDWR | O_NONBLOCK | O_CREAT, 0666, &mq_attr);
if (fd < 0) {
printf("ERROR: unable to create MQ, %d\n", -errno);
exit(-1);
}
sysc_meas_init(&sm_rx);
sysc_meas_init(&sm_tx);
dummy[0] = 0;
dummy[sizeof(dummy) - 1] = 0;
while (count--) {
ts = __cputime_get();
mq_send(fd, dummy, sizeof(dummy), 0);
sysc_meas_add(&sm_tx, __cputime_get() - ts);
ts = __cputime_get();
mq_receive(fd, dummy, sizeof(dummy), NULL);
sysc_meas_add(&sm_rx, __cputime_get() - ts);
}
mq_close(fd);
mq_unlink("/sysc_mq");
printf("RX: %ld/%ld/%ld\n", __cputime_ns(sm_rx.min),
__cputime_ns(sm_rx.sum / sm_rx.count),
__cputime_ns(sm_rx.max));
printf("TX: %ld/%ld/%ld\n", __cputime_ns(sm_tx.min),
__cputime_ns(sm_tx.sum / sm_tx.count),
__cputime_ns(sm_tx.max));
}
int main(int argc, char *argv[])
{
uint32_t loops = 100000, cnt;
uint64_t ts_a, ts_b, acc = 0;
if (argc > 1)
loops = strtoul(argv[1], (char **)NULL, 0);
cnt = loops;
sysc_mq(loops);
while (loops--) {
ts_a = __cputime_get();
(void)getppid();
ts_b = __cputime_get();
acc += (ts_b - ts_a);
}
printf("Accumulated time for %d getppid, %luns\n",
cnt, __cputime_ns(acc));
printf("Average time per getppid: %luns\n", (__cputime_ns(acc)/cnt));
exit (0);
}
Complete bisect result:
=======================
commit 10befea91b61c4e2c2d1df06a2e978d182fcf792 (HEAD, refs/bisect/bad)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:27 2020 -0700
mm: memcg/slab: use a single set of kmem_caches for all allocations
commit 15999eef7f25e2ea6a1c33f026166f472c5714e9 (refs/bisect/skip-15999eef7f25e2ea6a1c33f026166f472c5714e9)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:24 2020 -0700
mm: memcg/slab: remove redundant check in memcg_accumulate_slabinfo()
commit c7094406fcb7cdf4fe1de8893f0613b75349773d (refs/bisect/skip-c7094406fcb7cdf4fe1de8893f0613b75349773d)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:20 2020 -0700
mm: memcg/slab: deprecate slab_root_caches
commit 272911a4ad18c48f8bc449a5db945a54987dd687 (refs/bisect/skip-272911a4ad18c48f8bc449a5db945a54987dd687)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:17 2020 -0700
mm: memcg/slab: remove memcg_kmem_get_cache()
commit d797b7d05405c519f7b62ea69a75cea1883863b2 (refs/bisect/skip-d797b7d05405c519f7b62ea69a75cea1883863b2)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:14 2020 -0700
mm: memcg/slab: simplify memcg cache creation
commit 9855609bde03e2472b99a95e869d29ee1e78a751 (refs/bisect/skip-9855609bde03e2472b99a95e869d29ee1e78a751)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:10 2020 -0700
mm: memcg/slab: use a single set of kmem_caches for all accounted allocations
commit 0f876e4dc55db5fafef774917fd66e1373c0f390 (refs/bisect/skip-0f876e4dc55db5fafef774917fd66e1373c0f390)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:06 2020 -0700
mm: memcg/slab: move memcg_kmem_bypass() to memcontrol.h
commit 4330a26bc4527f1d8918c398ebc983574f761cca (refs/bisect/skip-4330a26bc4527f1d8918c398ebc983574f761cca)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:21:03 2020 -0700
mm: memcg/slab: deprecate memory.kmem.slabinfo
commit f2fe7b09a52bc898ec030d4fa6f78725439c7c2c (refs/bisect/skip-f2fe7b09a52bc898ec030d4fa6f78725439c7c2c)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:20:59 2020 -0700
mm: memcg/slab: charge individual slab objects instead of pages
commit 964d4bd370d559d9bd8e4abc139e85d2753956fb (refs/bisect/skip-964d4bd370d559d9bd8e4abc139e85d2753956fb)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:20:56 2020 -0700
mm: memcg/slab: save obj_cgroup for non-root slab objects
commit 286e04b8ed7a04279ae277f0f024430246ea5eec (refs/bisect/good-286e04b8ed7a04279ae277f0f024430246ea5eec)
Author: Roman Gushchin <guro@xxxxxx>
Date: Thu Aug 6 23:20:52 2020 -0700
mm: memcg/slab: allocate obj_cgroups for non-root slab pages
