Re: [PATCH v7 1/2] VT-d: Reduce spin timeout to 1ms, which can be boot-time changed

From: "Jan Beulich" <JBeulich@suse.com>
To: Quan Xu <quan.xu@intel.com>
Cc: "dario.faggioli@citrix.com" <dario.faggioli@citrix.com>,
	Feng Wu <feng.wu@intel.com>, Kevin Tian <kevin.tian@intel.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [PATCH v7 1/2] VT-d: Reduce spin timeout to 1ms, which can be boot-time changed
Date: Thu, 17 Mar 2016 02:13:53 -0600	[thread overview]
Message-ID: <56EA755102000078000DD997@prv-mh.provo.novell.com> (raw)
In-Reply-To: <945CA011AD5F084CBEA3E851C0AB28894B866025@SHSMSX101.ccr.corp.intel.com>

>>> On 17.03.16 at 09:11, <quan.xu@intel.com> wrote:
> On March 17, 2016 3:45pm, Tian, Kevin <kevin.tian@intel.com> wrote:
>> > From: Xu, Quan
>> > Sent: Thursday, March 17, 2016 3:13 PM diff --git
>> > a/xen/drivers/passthrough/vtd/qinval.c
>> > b/xen/drivers/passthrough/vtd/qinval.c
>> > index b81b0bd..37a15fb 100644
>> > --- a/xen/drivers/passthrough/vtd/qinval.c
>> > +++ b/xen/drivers/passthrough/vtd/qinval.c
>> > @@ -28,6 +28,11 @@
>> >  #include "vtd.h"
>> >  #include "extern.h"
>> >
>> > +static unsigned int __read_mostly vtd_qi_timeout = 1;
>> > +integer_param("vtd_qi_timeout", vtd_qi_timeout);
>> > +
>> > +#define IOMMU_QI_TIMEOUT (vtd_qi_timeout * MILLISECS(1))
>> > +
>> >  static void print_qi_regs(struct iommu *iommu)  {
>> >      u64 val;
>> > @@ -130,10 +135,14 @@ static void queue_invalidate_iotlb(struct iommu
>> *iommu,
>> >      spin_unlock_irqrestore(&iommu->register_lock, flags);  }
>> >
>> > +/*
>> > + * NB. We must check all kinds of error and all the way up the
>> > + * call trees.
>> > + */
>> 
>> This comment is meaningless put in the code. It just reflects what you need 
> do
>> to push the whole patch series, but it's obvious a straightforward 
> requirement.
>> 
> Kevin,
> This is for Jan requirement:
>           
> http://lists.xenproject.org/archives/html/xen-devel/2016-02/msg02388.html 
> Jan said: 
> """ Without a __must_check annotation on the function I cannot see
> how I should reasonably convince myself that all call sites now
> handle such an error in one way or another."""
> 
> Now I think I misunderstood what Jan said. It may be:
> 
> + static int __must_check queue_invalidate_wait(struct iommu *iommu, u8 
> iflag, u8 sw, u8 fn)
> 
> I found that there is a '__must_check' in xen code.

Indeed that's what I meant.

Jan

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