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

["Li,Rongqing" <lirongqing@baidu.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.
> 

Seems complex

I free this log is useless; since iommu_group_alloc_device only allocates device and sysfs, not attach group domain currently.
If failed, " Failed to add to iommu group " will be printed, it is more important to notice user.


-Li



> > > 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