Messages in this thread | | | Subject | Re: [RESEND PATCH v3 3/4] iommu/iova: Flush CPU rcache for when a depot fills | From | John Garry <> | Date | Wed, 9 Dec 2020 11:22:45 +0000 |
| |
On 09/12/2020 09:13, Leizhen (ThunderTown) wrote: > > > On 2020/11/17 18:25, John Garry wrote: >> Leizhen reported some time ago that IOVA performance may degrade over time >> [0], but unfortunately his solution to fix this problem was not given >> attention. >> >> To summarize, the issue is that as time goes by, the CPU rcache and depot >> rcache continue to grow. As such, IOVA RB tree access time also continues >> to grow. >> >> At a certain point, a depot may become full, and also some CPU rcaches may >> also be full when inserting another IOVA is attempted. For this scenario, >> currently the "loaded" CPU rcache is freed and a new one is created. This >> freeing means that many IOVAs in the RB tree need to be freed, which >> makes IO throughput performance fall off a cliff in some storage scenarios: >> >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6314MB/0KB/0KB /s] [1616K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [5669MB/0KB/0KB /s] [1451K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6031MB/0KB/0KB /s] [1544K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6673MB/0KB/0KB /s] [1708K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6705MB/0KB/0KB /s] [1717K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6031MB/0KB/0KB /s] [1544K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6761MB/0KB/0KB /s] [1731K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6705MB/0KB/0KB /s] [1717K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6685MB/0KB/0KB /s] [1711K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6178MB/0KB/0KB /s] [1582K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [6731MB/0KB/0KB /s] [1723K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [2387MB/0KB/0KB /s] [611K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [2689MB/0KB/0KB /s] [688K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [2278MB/0KB/0KB /s] [583K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [1288MB/0KB/0KB /s] [330K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [1632MB/0KB/0KB /s] [418K/0/0 iops] >> Jobs: 12 (f=12): [RRRRRRRRRRRR] [0.0% done] [1765MB/0KB/0KB /s] [452K/0/0 iops] >> >> And continue in this fashion, without recovering. Note that in this >> example it was required to wait 16 hours for this to occur. Also note that >> IO throughput also becomes gradually becomes more unstable leading up to >> this point. >> >> This problem is only seen for non-strict mode. For strict mode, the rcaches >> stay quite compact. >> >> As a solution to this issue, judge that the IOVA caches have grown too big >> when cached magazines need to be free, and just flush all the CPUs rcaches >> instead. >> >> The depot rcaches, however, are not flushed, as they can be used to >> immediately replenish active CPUs. >> >> In future, some IOVA compaction could be implemented to solve the >> instabilty issue, which I figure could be quite complex to implement. >> >> [0] https://lore.kernel.org/linux-iommu/20190815121104.29140-3-thunder.leizhen@huawei.com/ >> >> Analyzed-by: Zhen Lei <thunder.leizhen@huawei.com> >> Reported-by: Xiang Chen <chenxiang66@hisilicon.com> >> Signed-off-by: John Garry <john.garry@huawei.com>
Thanks for having a look
>> --- >> drivers/iommu/iova.c | 16 ++++++---------- >> 1 file changed, 6 insertions(+), 10 deletions(-) >> >> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c >> index 1f3f0f8b12e0..386005055aca 100644 >> --- a/drivers/iommu/iova.c >> +++ b/drivers/iommu/iova.c >> @@ -901,7 +901,6 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, >> struct iova_rcache *rcache, >> unsigned long iova_pfn) >> { >> - struct iova_magazine *mag_to_free = NULL; >> struct iova_cpu_rcache *cpu_rcache; >> bool can_insert = false; >> unsigned long flags; >> @@ -923,13 +922,12 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, >> if (cpu_rcache->loaded) >> rcache->depot[rcache->depot_size++] = >> cpu_rcache->loaded; >> - } else { >> - mag_to_free = cpu_rcache->loaded; >> + can_insert = true; >> + cpu_rcache->loaded = new_mag; >> } >> spin_unlock(&rcache->lock); >> - >> - cpu_rcache->loaded = new_mag; >> - can_insert = true; >> + if (!can_insert) >> + iova_magazine_free(new_mag); >> } >> } >> >> @@ -938,10 +936,8 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, >> >> spin_unlock_irqrestore(&cpu_rcache->lock, flags); >> >> - if (mag_to_free) { >> - iova_magazine_free_pfns(mag_to_free, iovad); >> - iova_magazine_free(mag_to_free); > mag_to_free has been stripped out, that's why lock protection is not required here. > >> - } >> + if (!can_insert) >> + free_all_cpu_cached_iovas(iovad); > Lock protection required.
But we have the per-CPU rcache locking again in free_cpu_cached_iovas() (which is called per-CPU from free_all_cpu_cached_iovas()).
ok? Or some other lock you mean?
Cheers, John
> >> >> return can_insert; >> } >> > > . >
| |