Re: 答复: [外部邮件] Re: [PATCH] iommu: Downgrade print level for iommu group information

[Pranjal Shrivastava <praan@google.com>]

On Tue, Nov 26, 2024 at 12:09:03PM +0000, Li,Rongqing wrote:
> 
> > On 26/11/2024 7:23 am, Li RongQing wrote:
> > > This per device log is becoming longer with more and more PCI devices
> > > in system, which slows down the boot process due to the serializing
> > > nature of printk().
> > >
> > > Downgrade dev_info() to dev_dbg() so it is still accessible for debug
> > > purposes.
> > 
> > Previously discussed 4 and a half years ago:
> > 
> > https://lore.kernel.org/linux-iommu/20200302154426.GC6540@8bytes.org/
> > 

Hmm.. I'm wondering if ratelimiting might help here? 
We can define a rate_limit for the iommu subsystem that can be tuned
accordingly to control verbosity. We can keep the rate_limit to a min.
as we'd like and maintain it upstream and give users an option to tune
it as per their requirement.

> > Also, given that the iommu_probe_device() path is inherently serialised anyway,
> > if logging a message from there significantly slows down your boot process, how
> > slow is your console device?
> > 
> 
> 
> There are 482 in my machine, spends nearly about 3 seconds
> 
> [   40.083614] DMAR: dmar1: Using Queued invalidation
> [   40.089008] DMAR: dmar0: Using Queued invalidation
> [   40.094402] DMAR: dmar19: Using Queued invalidation
> [   40.100816] pci 0000:79:00.4: Adding to iommu group 0
> [   40.106586] pci 0000:79:01.0: Adding to iommu group 1
> [   40.112346] pci 0000:79:02.0: Adding to iommu group 2
> [   40.118315] pci 0000:74:00.4: Adding to iommu group 3
> [   40.124074] pci 0000:74:01.0: Adding to iommu group 4
> [   40.129830] pci 0000:74:02.0: Adding to iommu group 5
------------------------------->8-----------------------------
			snip
------------------------------->8-----------------------------
> [   43.140538] pci 0000:ff:1e.6: Adding to iommu group 482
> [   43.146522] pci 0000:ff:1e.7: Adding to iommu group 482
> [   43.153222] DMAR: Intel(R) Virtualization Technology for Directed I/O
> [   43.160471] PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
> [   43.167715] software IO TLB: mapped [mem 0x000000006123e000-0x000000006523e000] (64MB)
> [   43.178633] RAPL PMU: API unit is 2^-32 Joules, 3 fixed counters, 655360 ms ovfl timer
> [   43.187540] RAPL PMU: hw unit of domain package 2^-14 Joules
> [   43.193906] RAPL PMU: hw unit of domain dram 2^-14 Joules
> [   43.199984] RAPL PMU: hw unit of domain psys 2^-0 Joules
> 

Thanks,
Praan