Re: [PATCH 1/4] Intel pci: Remove Host Bridge devices from identitymapping
From: Chris Wright
Date: Wed Mar 30 2011 - 15:58:02 EST
* Mike Travis (travis@xxxxxxx) wrote:
> Chris Wright wrote:
> >OK, I was actually interested in the !pt case. But this is useful
> >still. The iova lookup being distinct from the identity_mapping() case.
>
> I can get that as well, but having every device using maps caused it's
> own set of problems (hundreds of dma maps). Here's a list of devices
> on the system under test. You can see that even 'minor' glitches can
> get magnified when there are so many...
Yeah, I was focused on the overhead of actually mapping/unmapping an
address in the non-pt case.
> Blade Location NASID PCI Address X Display Device
> ----------------------------------------------------------------------
> 0 r001i01b00 0 0000:01:00.0 - Intel 82576 Gigabit Network Connection
> . . . 0000:01:00.1 - Intel 82576 Gigabit Network Connection
> . . . 0000:04:00.0 - LSI SAS1064ET Fusion-MPT SAS
> . . . 0000:05:00.0 - Matrox MGA G200e
> 2 r001i01b02 4 0001:02:00.0 - Mellanox MT26428 InfiniBand
> 3 r001i01b03 6 0002:02:00.0 - Mellanox MT26428 InfiniBand
> 4 r001i01b04 8 0003:02:00.0 - Mellanox MT26428 InfiniBand
> 11 r001i01b11 22 0007:02:00.0 - Mellanox MT26428 InfiniBand
> 13 r001i01b13 26 0008:02:00.0 - Mellanox MT26428 InfiniBand
> 15 r001i01b15 30 0009:07:00.0 :0.0 nVidia GF100 [Tesla S2050]
> . . . 0009:08:00.0 :1.1 nVidia GF100 [Tesla S2050]
> 18 r001i23b02 36 000b:02:00.0 - Mellanox MT26428 InfiniBand
> 20 r001i23b04 40 000c:01:00.0 - Intel 82599EB 10-Gigabit Network Connection
> . . . 000c:01:00.1 - Intel 82599EB 10-Gigabit Network Connection
> . . . 000c:04:00.0 - Mellanox MT26428 InfiniBand
> 23 r001i23b07 46 000d:07:00.0 - nVidia GF100 [Tesla S2050]
> . . . 000d:08:00.0 - nVidia GF100 [Tesla S2050]
> 25 r001i23b09 50 000e:01:00.0 - Intel 82599EB 10-Gigabit Network Connection
> . . . 000e:01:00.1 - Intel 82599EB 10-Gigabit Network Connection
> . . . 000e:04:00.0 - Mellanox MT26428 InfiniBand
> 26 r001i23b10 52 000f:02:00.0 - Mellanox MT26428 InfiniBand
> 27 r001i23b11 54 0010:02:00.0 - Mellanox MT26428 InfiniBand
> 29 r001i23b13 58 0011:02:00.0 - Mellanox MT26428 InfiniBand
> 31 r001i23b15 62 0012:02:00.0 - Mellanox MT26428 InfiniBand
> 34 r002i01b02 68 0013:01:00.0 - Mellanox MT26428 InfiniBand
> 35 r002i01b03 70 0014:02:00.0 - Mellanox MT26428 InfiniBand
> 36 r002i01b04 72 0015:01:00.0 - Mellanox MT26428 InfiniBand
> 41 r002i01b09 82 0018:07:00.0 - nVidia GF100 [Tesla S2050]
> . . . 0018:08:00.0 - nVidia GF100 [Tesla S2050]
> 43 r002i01b11 86 0019:01:00.0 - Mellanox MT26428 InfiniBand
> 45 r002i01b13 90 001a:01:00.0 - Mellanox MT26428 InfiniBand
> 48 r002i23b00 96 001c:07:00.0 - nVidia GF100 [Tesla S2050]
> . . . 001c:08:00.0 - nVidia GF100 [Tesla S2050]
> 50 r002i23b02 100 001d:02:00.0 - Mellanox MT26428 InfiniBand
> 52 r002i23b04 104 001e:01:00.0 - Intel 82599EB 10-Gigabit Network Connection
> . . . 001e:01:00.1 - Intel 82599EB 10-Gigabit Network Connection
> . . . 001e:04:00.0 - Mellanox MT26428 InfiniBand
> 57 r002i23b09 114 0020:01:00.0 - Intel 82599EB 10-Gigabit Network Connection
> . . . 0020:01:00.1 - Intel 82599EB 10-Gigabit Network Connection
> . . . 0020:04:00.0 - Mellanox MT26428 InfiniBand
> 58 r002i23b10 116 0021:02:00.0 - Mellanox MT26428 InfiniBand
> 59 r002i23b11 118 0022:02:00.0 - Mellanox MT26428 InfiniBand
> 61 r002i23b13 122 0023:02:00.0 - Mellanox MT26428 InfiniBand
> 63 r002i23b15 126 0024:02:00.0 - Mellanox MT26428 InfiniBand
>
> >
> >>uv48-sys was receiving and uv-debug sending.
> >>ksoftirqd/640 was running at approx. 100% cpu utilization.
> >>I had pinned the nttcp process on uv48-sys to cpu 64.
> >>
> >># Samples: 1255641
> >>#
> >># Overhead Command Shared Object Symbol
> >># ........ ............. ............. ......
> >>#
> >> 50.27%ESC[m ksoftirqd/640 [kernel] [k] _spin_lock
> >> 27.43%ESC[m ksoftirqd/640 [kernel] [k] iommu_no_mapping
> >
> >>...
> >> 0.48% ksoftirqd/640 [kernel] [k] iommu_should_identity_map
> >> 0.45% ksoftirqd/640 [kernel] [k] ixgbe_alloc_rx_buffers [
> >>ixgbe]
> >
> >Note, ixgbe has had rx dma mapping issues (that's why I wondered what
> >was causing the massive slowdown under !pt mode).
>
> I think since this profile run, the network guys updated the ixgbe
> driver with a later version. (I don't know the outcome of that test.)
OK. The ixgbe fix I was thinking of is in since 2.6.34: 43634e82 (ixgbe:
Fix DMA mapping/unmapping issues when HWRSC is enabled on IOMMU enabled
on IOMMU enabled kernels).
> ><snip>
> >>I tracked this time down to identity_mapping() in this loop:
> >>
> >> list_for_each_entry(info, &si_domain->devices, link)
> >> if (info->dev == pdev)
> >> return 1;
> >>
> >>I didn't get the exact count, but there was approx 11,000 PCI devices
> >>on this system. And this function was called for every page request
> >>in each DMA request.
> >
> >Right, so this is the list traversal (and wow, a lot of PCI devices).
>
> Most of the PCI devices were the 45 on each of 256 Nahalem sockets.
> Also, there's a ton of bridges as well.
>
> >Did you try a smarter data structure? (While there's room for another
> >bit in pci_dev, the bit is more about iommu implementation details than
> >anything at the pci level).
> >
> >Or the domain_dev_info is cached in the archdata of device struct.
> >You should be able to just reference that directly.
> >
> >Didn't think it through completely, but perhaps something as simple as:
> >
> > return pdev->dev.archdata.iommu == si_domain;
>
> I can try this, thanks!
Err, I guess that'd be info = archdata.iommu; info->domain == si_domain
(and probably need some sanity checking against things like
DUMMY_DEVICE_DOMAIN_INFO). But you get the idea.
thanks,
-chris
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/