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"