Re: [External] Re: [PATCH v2] iommu/iova: Optimize alloc_iova with rbtree_augmented
From: Ethan Zhao
Date: Fri Aug 26 2022 - 04:58:57 EST
Peng,
在 2022/8/25 16:10, Peng Zhang 写道:
Hi,
Here is a real example. The version of kernel is 5.4.56.
Occurs when a lot of iova are not released for a long time.
[Wed May 25 05:27:59 2022] watchdog: BUG: soft lockup - CPU#58 stuck
for 23s! [ksoftirqd/58:302]
[Wed May 25 05:27:59 2022] Call Trace:
[Wed May 25 05:27:59 2022] alloc_iova+0xf2/0x140
[Wed May 25 05:27:59 2022] alloc_iova_fast+0x56/0x251
The rcache doesn't work at all , the worst case.
[Wed May 25 05:27:59 2022] dma_ops_alloc_iova.isra.27+0x4b/0x70
[Wed May 25 05:27:59 2022] __map_single.isra.28+0x4a/0x1d0
[Wed May 25 05:27:59 2022] mlx5e_sq_xmit+0x98d/0x12b0 [mlx5_core]
[Wed May 25 05:27:59 2022] ? packet_rcv+0x43/0x460
[Wed May 25 05:27:59 2022] ? dev_hard_start_xmit+0x90/0x1e0
[Wed May 25 05:27:59 2022] ? sch_direct_xmit+0x111/0x320
[Wed May 25 05:27:59 2022] ? __qdisc_run+0x143/0x540
[Wed May 25 05:27:59 2022] ? __dev_queue_xmit+0x6c3/0x8e0
[Wed May 25 05:27:59 2022] ? ip_finish_output2+0x2d5/0x580
[Wed May 25 05:27:59 2022] ? __ip_finish_output+0xe9/0x1b0
[Wed May 25 05:27:59 2022] ? ip_output+0x6c/0xe0
[Wed May 25 05:27:59 2022] ? __ip_finish_output+0x1b0/0x1b0
[Wed May 25 05:27:59 2022] ? __ip_queue_xmit+0x15d/0x420
[Wed May 25 05:27:59 2022] ? __tcp_transmit_skb+0x405/0x600
[Wed May 25 05:27:59 2022] ? tcp_delack_timer_handler+0xb7/0x1b0
[Wed May 25 05:27:59 2022] ? tcp_delack_timer+0x8b/0xa0
[Wed May 25 05:27:59 2022] ? tcp_delack_timer_handler+0x1b0/0x1b0
[Wed May 25 05:27:59 2022] ? call_timer_fn+0x2b/0x120
[Wed May 25 05:27:59 2022] ? run_timer_softirq+0x1a6/0x420
[Wed May 25 05:27:59 2022] ? update_load_avg+0x7e/0x640
[Wed May 25 05:27:59 2022] ? update_curr+0xe1/0x1d0
[Wed May 25 05:27:59 2022] ? __switch_to+0x7a/0x3e0
[Wed May 25 05:27:59 2022] ? __do_softirq+0xda/0x2da
[Wed May 25 05:27:59 2022] ? sort_range+0x20/0x20
[Wed May 25 05:27:59 2022] ? run_ksoftirqd+0x26/0x40
[Wed May 25 05:27:59 2022] ? smpboot_thread_fn+0xb8/0x150
[Wed May 25 05:27:59 2022] ? kthread+0x110/0x130
[Wed May 25 05:27:59 2022] ? kthread_park+0x80/0x80
[Wed May 25 05:27:59 2022] ? ret_from_fork+0x1f/0x30
I did some more tests.
The test is single threaded.
Granule is 4k, limit is 2^20.
When the 1/4 address space is occupied by iova,
Repeat the following two steps：
1. Randomly releases an iova.
2. Allocate an iova of size 1 within the allocation limit of 2^20.
Before improvement:
Tracing 1 functions for "alloc_iova"... Hit Ctrl-C to end.
^C
nsecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 352
| |
512 -> 1023 : 258078
|****************************************|
1024 -> 2047 : 3612
| |
2048 -> 4095 : 426
| |
4096 -> 8191 : 183
| |
8192 -> 16383 : 6 | |
16384 -> 32767 : 5 | |
32768 -> 65535 : 9 | |
65536 -> 131071 : 18 | |
131072 -> 262143 : 28 | |
262144 -> 524287 : 74 | |
524288 -> 1048575 : 109
| |
1048576 -> 2097151 : 170
| |
2097152 -> 4194303 : 100
| |
4194304 -> 8388607 : 1 | |
avg = 3110 nsecs, total: 818614399 nsecs, count: 263171
Tracing 1 functions for "remove_iova"... Hit Ctrl-C to end.
^C
nsecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 250651
|****************************************|
512 -> 1023 : 12405
|* |
1024 -> 2047 : 111
| |
2048 -> 4095 : 1 | |
avg = 433 nsecs, total: 114136319 nsecs, count: 263168
With improvement:
Tracing 1 functions for "alloc_iova"... Hit Ctrl-C to end.
^C
nsecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 258975
|****************************************|
1024 -> 2047 : 3618
| |
2048 -> 4095 : 497
| |
4096 -> 8191 : 74 | |
8192 -> 16383 : 4 | |
16384 -> 32767 : 1 | |
avg = 637 nsecs, total: 167854061 nsecs, count: 263169
Tracing 1 functions for "remove_iova"... Hit Ctrl-C to end.
^C
nsecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 221560
|****************************************|
512 -> 1023 : 41427
|******* |
1024 -> 2047 : 179
| |
2048 -> 4095 : 2 | |
avg = 477 nsecs, total: 125540399 nsecs, count: 263168
Though only 3-4 drivers use alloc_iova() directly, in my understanding
your test has simulated the worst case, rcache doesn't work at all,
"alloc_iova" +“remove_iova” number looks great for worst case.
Reviewed-by: Ethan Zhao <haifeng.zhao@xxxxxxxxxxxxxxx>
s/distbution/distribution ?
Sorry, it's a typo.
I don't have a test program for "alloc_iova_fast + free_iova_fast"
right now.
Thanks,
Peng
--
"firm, enduring, strong, and long-lived"