On 2022-03-03 03:43, yf.wang@xxxxxxxxxxxx wrote:
On Thu, 2022-03-03 at 07:52 +0800, Miles Chen wrote:
Thanks for your explanation.
YF showed me some numbers yesterday and maybe we can have a further
discussion in that test case. (It looks like that some iovas are
freed but
their pfn_lo(s) are less than cached_iova->pfn_lo, so
max32_alloc_size is not
reset. So there are enought free iovas but the allocation still
failed)
__cached_rbnode_delete_update(struct iova_domain *iovad, struct iova
*free)
{
struct iova *cached_iova;
cached_iova = to_iova(iovad->cached32_node);
if (free == cached_iova ||
(free->pfn_hi < iovad->dma_32bit_pfn &&
free->pfn_lo >= cached_iova->pfn_lo)) {
iovad->cached32_node = rb_next(&free->node);
iovad->max32_alloc_size = iovad->dma_32bit_pfn;
}
...
}
Hi YF,
Could your share your observation of the iova allocation failure you
hit?
Thanks,
Miles
Hi Miles & Robin,
The scenario we encountered in our actual test:
An iova domain with a 3GB iova region (0x4000_0000~0x1_0000_0000),
only alloc iova total size 614788KB), then alloc iova size=0x731f000
fail, and then the retry mechanism is free 300 cache iova at first,
and then retry still fail, the reason for fail is blocked by the
check condition (size >= iovad->max32_alloc_size) and goto iova32_full
directly.
Why is no reset max32_alloc_size in __cached_rbnode_delete_update?
Because of the pfn_lo of the freed cache iova is smaller than the
current cached32_node's pfn_lo (free->pfn_lo < cached_iova->pfn_lo),
so will not execute (iovad->max32_alloc_size = iovad->dma_32bit_pfn),
is blocked by the check condition (free->pfn_lo >= cached_iova-
pfn_lo).
The issue observed during stress testing, when alloc fail reset
max32_alloc_size to retry can help to allocate iova to those lower
addresses.
Oh, now I see what's going on, thanks for clarifying. This is a
wonderfully obscure corner case, but ultimately what comes out of it is
that there's an assumption in __cached_rbnode_delete_update() which I
think was OK at the time it was written (due to other limitations), but
now deserves to be remedied.
The proper fix is simple to make, but I think I'll need to have my lunch
before trying to write up the reasoning behind it for a patch... :)
Thanks,
Robin.
The following is the actual stress test log dump:
('pfn_lo', 'size' and 'pfn_hi' has iova_shift in dump log)
size: 0x731f000
max32_alloc_size: 0x731f000
cached_iova: 0xffffff814751a1c0
cached_iova->pfn_lo: 0xf3500000
cached_iova->pfn_hi: 0xf35ff000
1.__alloc_and_insert_iova_range_fail
[name:iova&]__alloc_and_insert_iova_range_fail:
iovad:0xffffff80d5be2808
{granule:0x1000, start_pfn:0x40000, dma_32bit_pfn:0x100000,
max32_alloc_size:0x731f},size:0x731f
2.dump all iova nodes of rbtree, contain cached iova:
[name:iova&]dump_iova_rbtree start, iovad:0xffffff80d5be2808
{rbroot:0xffffff814751a4c0, cached_node:0xffffff80d5be2860,
cached32_node:0xffffff814751a1c0, granule:0x1000, start_pfn:0x40000,
dma_32bit_pfn:0x100000, max32_alloc_size:0x731f}
('pfn_lo', 'size' and 'pfn_hi' has iova_shift in dump log)
[name:iova&]index iova_object pfn_lo size pfn_hi
[name:iova&] 1 0xffffff814751ae00 0x40800000 0x4c9000 0x40cc8000
[name:iova&] 2 0xffffff807c960880 0x40d00000 0xc4000 0x40dc3000
...322 lines of log are omitted here...
[name:iova&]325 0xffffff814751a1c0 0xf3500000 0x100000 0xf35ff000
[name:iova&]326 0xffffff8004552080 0xf3600000 0x100000 0xf36ff000
[name:iova&]327 0xffffff80045524c0 0xf3700000 0xbc000 0xf37bb000
[name:iova&]328 0xffffff814751a700 0xf3800000 0x265000 0xf3a64000
[name:iova&]329 0xffffff8004552180 0xf3c00000 0xa13000 0xf4612000
[name:iova&]330 0xffffff80c1b3eb40 0xf4800000 0xb400000 0xffbff000
[name:iova&]331 0xffffff80d6e0b580 0xffcff000 0x1000 0xffcff000
[name:iova&]332 0xffffff80c8395140 0xffd00000 0x80000 0xffd7f000
[name:iova&]333 0xffffff80c8395000 0xffde0000 0x20000 0xffdff000
[name:iova&]334 0xffffff80c8395380 0xffe00000 0x80000 0xffe7f000
[name:iova&]335 0xffffff80c8395880 0xffec0000 0x20000 0xffedf000
[name:iova&]336 0xffffff80c83957c0 0xffef9000 0x1000 0xffef9000
[name:iova&]337 0xffffff80c83956c0 0xffefa000 0x1000 0xffefa000
[name:iova&]338 0xffffff80c8395f40 0xffefb000 0x1000 0xffefb000
[name:iova&]339 0xffffff80c8395a80 0xffefc000 0x4000 0xffeff000
[name:iova&]340 0xffffff80c1b3e840 0xfff00000 0x100000 0xfffff000
[name:iova&] 41 0xffffff80d5be2860 0xfffffffffffff000 0x1000
0xfffffffffffff000
[name:iova&]dump_iova_rbtree done, iovad:0xffffff80d5be2808,
count:341, total_size:625876KB
3.alloc fail, flushing rcache and retry.
[name:iova&]alloc_iova_fast, flushing rcache and retry,
iovad:0xffffff80d5be2808, size:0x731f, limit_pfn:0xfffff
4.retry is executed into the __alloc_and_insert_iova_range function:
[name:iova&]__alloc_and_insert_iova_range fail goto iova32_full,
iovad:0xffffff80d5be2808 {granule:0x1000, start_pfn:0x40000,
dma_32bit_pfn:0x100000, max32_alloc_size:0x731f},size:0x731f
5.dump all iova nodes of rbtree, current caches is already empty:
[name:iova&]dump_iova_rbtree start, iovad:0xffffff80d5be2808
{rbroot:0xffffff80fe76da80, cached_node:0xffffff80d5be2860,
cached32_node:0xffffff814751a1c0, granule:0x1000, start_pfn:0x40000,
dma_32bit_pfn:0x100000, max32_alloc_size:0x731f}
('pfn_lo', 'size' and 'pfn_hi' has iova_shift in dump log)
[name:iova&]index iova_object pfn_lo size pfn_hi
[name:iova&] 1 0xffffff814751ae00 0x40800000 0x4c9000 0x40cc8000
[name:iova&] 2 0xffffff807c960880 0x40d00000 0xc4000 0x40dc3000
[name:iova&] 3 0xffffff81487ce840 0x40e00000 0x37a000 0x41179000
[name:iova&] 4 0xffffff80fe76d600 0x41200000 0x2400000 0x435ff000
[name:iova&] 5 0xffffff8004552000 0x46800000 0x47e2000 0x4afe1000
[name:iova&] 6 0xffffff807c960a40 0x50200000 0x400000 0x505ff000
[name:iova&] 7 0xffffff818cdb5780 0x50600000 0x265000 0x50864000
[name:iova&] 8 0xffffff814751a440 0x50a00000 0x2ae000 0x50cad000
[name:iova&] 9 0xffffff818cdb5d40 0x50e00000 0x4c9000 0x512c8000
[name:iova&] 10 0xffffff81487cef40 0x51400000 0x1a25000 0x52e24000
[name:iova&] 11 0xffffff818cdb5140 0x53c00000 0x400000 0x53fff000
[name:iova&] 12 0xffffff814751a7c0 0x54000000 0x400000 0x543ff000
[name:iova&] 13 0xffffff80fe76d2c0 0x54500000 0xbc000 0x545bb000
[name:iova&] 14 0xffffff81487ce0c0 0x54600000 0x400000 0x549ff000
[name:iova&] 15 0xffffff80fe76d740 0x54a00000 0xbc000 0x54abb000
[name:iova&] 16 0xffffff8004552440 0x54b00000 0xbc000 0x54bbb000
[name:iova&] 17 0xffffff80fe76db80 0x54c00000 0x47e2000 0x593e1000
[name:iova&] 18 0xffffff818cdb5440 0x65000000 0x400000 0x653ff000
[name:iova&] 19 0xffffff8004552880 0x65400000 0x47e2000 0x69be1000
[name:iova&] 20 0xffffff814751acc0 0x6c7e0000 0x20000 0x6c7ff000
[name:iova&] 21 0xffffff80fe76d700 0x6c800000 0x47e2000 0x70fe1000
//0x70fe1000 - 0xebc00000 = 0x7ac1f000:This free range is large enough
[name:iova&] 22 0xffffff80fe76da80 0xebc00000 0x400000 0xebfff000
[name:iova&] 23 0xffffff80045523c0 0xec000000 0x400000 0xec3ff000
[name:iova&] 24 0xffffff8004552780 0xec400000 0x400000 0xec7ff000
[name:iova&] 25 0xffffff814751a1c0 0xf3500000 0x100000 0xf35ff000
[name:iova&] 26 0xffffff8004552080 0xf3600000 0x100000 0xf36ff000
[name:iova&] 27 0xffffff80045524c0 0xf3700000 0xbc000 0xf37bb000
[name:iova&] 28 0xffffff814751a700 0xf3800000 0x265000 0xf3a64000
[name:iova&] 29 0xffffff8004552180 0xf3c00000 0xa13000 0xf4612000
[name:iova&] 30 0xffffff80c1b3eb40 0xf4800000 0xb400000 0xffbff000
[name:iova&] 31 0xffffff80d6e0b580 0xffcff000 0x1000 0xffcff000
[name:iova&] 32 0xffffff80c8395140 0xffd00000 0x80000 0xffd7f000
[name:iova&] 33 0xffffff80c8395000 0xffde0000 0x20000 0xffdff000
[name:iova&] 34 0xffffff80c8395380 0xffe00000 0x80000 0xffe7f000
[name:iova&] 35 0xffffff80c8395880 0xffec0000 0x20000 0xffedf000
[name:iova&] 36 0xffffff80c83957c0 0xffef9000 0x1000 0xffef9000
[name:iova&] 37 0xffffff80c83956c0 0xffefa000 0x1000 0xffefa000
[name:iova&] 38 0xffffff80c8395f40 0xffefb000 0x1000 0xffefb000
[name:iova&] 39 0xffffff80c8395a80 0xffefc000 0x4000 0xffeff000
[name:iova&] 40 0xffffff80c1b3e840 0xfff00000 0x100000 0xfffff000
[name:iova&] 41 0xffffff80d5be2860 0xfffffffffffff000 0x1000
0xfffffffffffff000
[name:iova&]dump_iova_rbtree done, iovad:0xffffff80d5be2808,
count:41, total_size:614788KB
Thanks,
Yunfei.
