Messages in this thread | | | Date | Tue, 9 Nov 2021 21:32:19 +0100 | Subject | Re: How to reduce PCI initialization from 5 s (1.5 s adding them to IOMMU groups) | From | Paul Menzel <> |
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Dear Robin,
Thank you for your reply.
Am 09.11.21 um 16:31 schrieb Robin Murphy: > On 2021-11-06 10:42, Paul Menzel wrote:
>> Am 05.11.21 um 19:53 schrieb Bjorn Helgaas: >>> On Fri, Nov 05, 2021 at 12:56:09PM +0100, Paul Menzel wrote: >> >>>> On a PowerEdge T440/021KCD, BIOS 2.11.2 04/22/2021, Linux 5.10.70 takes >>>> almost five seconds to initialize PCI. According to the timestamps, >>>> 1.5 s >>>> are from assigning the PCI devices to the 142 IOMMU groups. >>>> >>>> ``` >>>> $ lspci | wc -l >>>> 281 >>>> $ dmesg >>>> […] >>>> [ 2.918411] PCI: Using host bridge windows from ACPI; if >>>> necessary, use "pci=nocrs" and report a bug >>>> [ 2.933841] ACPI: Enabled 5 GPEs in block 00 to 7F >>>> [ 2.973739] ACPI: PCI Root Bridge [PC00] (domain 0000 [bus 00-16]) >>>> [ 2.980398] acpi PNP0A08:00: _OSC: OS supports [ExtendedConfig ASPM ClockPM Segments MSI HPX-Type3] >>>> [ 2.989457] acpi PNP0A08:00: _OSC: platform does not support [LTR] >>>> [ 2.995451] acpi PNP0A08:00: _OSC: OS now controls [PME >>>> PCIeCapability] >>>> [ 3.001394] acpi PNP0A08:00: FADT indicates ASPM is unsupported, using BIOS configuration >>>> [ 3.010511] PCI host bridge to bus 0000:00 >>>> […] >>>> [ 6.233508] system 00:05: [io 0x1000-0x10fe] has been reserved >>>> [ 6.239420] system 00:05: Plug and Play ACPI device, IDs PNP0c02 (active) >>>> [ 6.239906] pnp: PnP ACPI: found 6 devices >>> >>> For ~280 PCI devices, (6.24-2.92)/280 = 0.012 s/dev. On my laptop I >>> have about (.66-.37)/36 = 0.008 s/dev (on v5.4), so about the same >>> ballpark. >> >> Though if it was on average 0.008 s/dev here, around a second could be >> saved. >> >> The integrated Matrox G200eW3 graphics controller (102b:0536) and the >> two Broadcom NetXtreme BCM5720 2-port Gigabit Ethernet PCIe cards >> (14e4:165f) take 150 ms to be initialized. >> >> [ 3.454409] pci 0000:03:00.0: [102b:0536] type 00 class 0x030000 >> [ 3.460411] pci 0000:03:00.0: reg 0x10: [mem 0x91000000-0x91ffffff pref] >> [ 3.467403] pci 0000:03:00.0: reg 0x14: [mem 0x92808000-0x9280bfff] >> [ 3.473402] pci 0000:03:00.0: reg 0x18: [mem 0x92000000-0x927fffff] >> [ 3.479437] pci 0000:03:00.0: BAR 0: assigned to efifb >> >> The timestamp in each line differs by around 6 ms. Could printing the >> messages to the console (VGA) hold this up (line 373 to line 911 makes >> (6.24 s-2.92 s)/(538 lines) = (3.32 s)/(538 lines) = 6 ms)? >> >> [ 3.484480] pci 0000:02:00.0: PCI bridge to [bus 03] >> [ 3.489401] pci 0000:02:00.0: bridge window [mem 0x92000000-0x928fffff] >> [ 3.496398] pci 0000:02:00.0: bridge window [mem 0x91000000-0x91ffffff 64bit pref] >> [ 3.504446] pci 0000:04:00.0: [14e4:165f] type 00 class 0x020000 >> [ 3.510415] pci 0000:04:00.0: reg 0x10: [mem 0x92e30000-0x92e3ffff 64bit pref] >> [ 3.517408] pci 0000:04:00.0: reg 0x18: [mem 0x92e40000-0x92e4ffff 64bit pref] >> [ 3.524407] pci 0000:04:00.0: reg 0x20: [mem 0x92e50000-0x92e5ffff 64bit pref] >> [ 3.532402] pci 0000:04:00.0: reg 0x30: [mem 0xfffc0000-0xffffffff pref] >> [ 3.538483] pci 0000:04:00.0: PME# supported from D0 D3hot D3cold >> [ 3.544437] pci 0000:04:00.0: 4.000 Gb/s available PCIe bandwidth, limited by 5.0 GT/s PCIe x1 link at 0000:00:1c.5 (capable of 8.000 Gb/s with 5.0 GT/s PCIe x2 link) >> [ 3.559493] pci 0000:04:00.1: [14e4:165f] type 00 class 0x020000 >> >> Here is a 15 ms delay. >> >> [ 3.565415] pci 0000:04:00.1: reg 0x10: [mem 0x92e00000-0x92e0ffff 64bit pref] >> [ 3.573407] pci 0000:04:00.1: reg 0x18: [mem 0x92e10000-0x92e1ffff 64bit pref] >> [ 3.580407] pci 0000:04:00.1: reg 0x20: [mem 0x92e20000-0x92e2ffff 64bit pref] >> [ 3.587402] pci 0000:04:00.1: reg 0x30: [mem 0xfffc0000-0xffffffff pref] >> [ 3.594483] pci 0000:04:00.1: PME# supported from D0 D3hot D3cold >> [ 3.600502] pci 0000:00:1c.5: PCI bridge to [bus 04] >> >> Can the 6 ms – also from your system – be explained by the PCI >> specification? Seeing how fast PCI nowadays is, 6 ms sounds like a >> long time. ;-) >> >>> Faster would always be better, of course. I assume this is not really >>> a regression? >> >> Correct, as far as I know of, this is no regression. >> >>>> [ 6.989016] pci 0000:d7:05.0: disabled boot interrupts on device [8086:2034] >>>> [ 6.996063] PCI: CLS 0 bytes, default 64 >>>> [ 7.000008] Trying to unpack rootfs image as initramfs... >>>> [ 7.065281] Freeing initrd memory: 5136K >> >> The PCI resource assignment(?) also seems to take 670 ms: >> >> [ 6.319656] pci 0000:04:00.0: can't claim BAR 6 [mem 0xfffc0000-0xffffffff pref]: no compatible bridge window >> […] >> [ 6.989016] pci 0000:d7:05.0: disabled boot interrupts on device [8086:2034] >> >>>> […] >>>> [ 7.079098] DMAR: dmar7: Using Queued invalidation >>>> [ 7.083983] pci 0000:00:00.0: Adding to iommu group 0 >>>> […] >>>> [ 8.537808] pci 0000:d7:17.1: Adding to iommu group 141 >>> >>> I don't have this iommu stuff turned on and don't know what's >>> happening here. >> >> There is a lock in `iommu_group_add_device()` in `drivers/iommu/iommu.c`: >> >> mutex_lock(&group->mutex); >> list_add_tail(&device->list, &group->devices); >> if (group->domain && !iommu_is_attach_deferred(group->domain, dev)) >> ret = __iommu_attach_device(group->domain, dev); >> mutex_unlock(&group->mutex); >> >> No idea, if it’s related. Unfortunately, it’s a production system, so >> I can’t do any debugging. (Maybe `initcall_debug` could give some >> insight.) Maybe the IOMMU developers can explain it without it. Could >> the IOMMU group assignment be done in parallel? > > FWIW I'd expect that locking to be pretty much immaterial - many devices > are getting their own uncontended groups, and callers of this tend to be > serialised at a higher level anyway. iommu_probe_device() usually runs > off the back of the device_add() notifier (where it could be that it's > the only thing making noise in between something *else* being slow), but > there is the special case where it gets replayed for all existing > devices when the IOMMU driver registers itself - at a guess it seems > like it may well be the latter case you're seeing, but either way > there's not much to say without figuring out where the time is actually > being spent (I don't suppose that machine has dynamic ftrace enabled?).
Our Linux kernel has dynamic ftrace enabled.
$ grep CONFIG_DYNAMIC_FTRACE /boot/config-5.10.70.mx64.403 CONFIG_DYNAMIC_FTRACE=y CONFIG_DYNAMIC_FTRACE_WITH_REGS=y CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS=y
> That said, setting up a new group isn't a completely insignificant > amount of work, and 142 groups seems a lot - I'd have assumed that a > system of that scale would be the kind of big server kit that takes > several minutes to boot to the point of even starting the kernel anyway.
You are right. As noted in my reply to Krzysztof, it’s more like a pet peeve, but is also relevant, when kexec is used.
Kind regards,
Paul
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