linux-kernel - Re: [PATCH v2 1/2] iommu/vt-d: Ratelimit fault handler

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Date:	Thu, 17 Mar 2016 14:46:39 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Joe Perches <joe@...ches.com>
Cc:	iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
	joro@...tes.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] iommu/vt-d: Ratelimit fault handler

On Thu, 17 Mar 2016 13:33:30 -0700
Joe Perches <joe@...ches.com> wrote:

> On Thu, 2016-03-17 at 14:12 -0600, Alex Williamson wrote:
> > Fault rates can easily overwhelm the console and make the system
> > unresponsive.  Ratelimit to allow an opportunity for maintenance.  
> []
> > diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c  
> []
> > @@ -1602,10 +1602,17 @@ irqreturn_t dmar_fault(int irq, void *dev_id)
> >  	int reg, fault_index;
> >  	u32 fault_status;
> >  	unsigned long flag;
> > +	bool ratelimited;
> > +	static DEFINE_RATELIMIT_STATE(rs,
> > +				      DEFAULT_RATELIMIT_INTERVAL,
> > +				      DEFAULT_RATELIMIT_BURST);  
> 
> Are these the appropriate limits for dmar?
> 
> include/linux/ratelimit.h:#define DEFAULT_RATELIMIT_INTERVAL    (5 * HZ)
> include/linux/ratelimit.h:#define DEFAULT_RATELIMIT_BURST       10

They seem OK to me, I've got a test running that continuously generates
DMA read faults and I get 20 lines of log every 5 seconds.  That seems
like enough to know there's an issue, it's ongoing, and maybe see some
patterns in the fault addresses.  I expect we could turn up the burst
value but generally when I'm looking at the logs I'm only looking for
things like is it a single target address, is it a sequential address,
or what's the general address space to know if it should or should not
be a valid fault address.  Thanks,

Alex