From: "Woods, Brian" <Brian.Woods@amd.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Jan Beulich" <JBeulich@suse.com>, "Wei Liu" <wl@xen.org>,
"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com>,
Xen-devel <xen-devel@lists.xenproject.org>,
"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
"Woods, Brian" <Brian.Woods@amd.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH] x86/AMD-Vi: Fold exit paths of {enable, disable}_iommu()
Date: Mon, 12 Aug 2019 18:01:06 +0000 [thread overview]
Message-ID: <20190812180101.GB1377@amd.com> (raw)
In-Reply-To: <20190812175205.29143-1-andrew.cooper3@citrix.com>
On Mon, Aug 12, 2019 at 06:52:05PM +0100, Andy Cooper wrote:
> ... to avoid having multiple spin_unlock_irqrestore() calls.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Brian Woods <brian.woods@amd.com>
> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wl@xen.org>
> CC: Roger Pau Monné <roger.pau@citrix.com>
> CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> CC: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> CC: Brian Woods <brian.woods@amd.com>
>
> Interestingly GCC 6.3 managed to fold disable_iommu() automatically. There is
> some partial folding for enable_iommu() (insofar as there is only a single
> call to _spin_unlock_irqrestore emitted), but this delta yeilds
>
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-20 (-20)
> Function old new delta
> enable_iommu 1844 1824 -20
> Total: Before=3340299, After=3340279, chg -0.00%
>
> which means that something wasn't done automatically.
>
> Noticed while investigating the S3 regression.
> ---
> xen/drivers/passthrough/amd/iommu_init.c | 17 +++++++----------
> 1 file changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/xen/drivers/passthrough/amd/iommu_init.c b/xen/drivers/passthrough/amd/iommu_init.c
> index bb9f33e264..bb5a3e57c9 100644
> --- a/xen/drivers/passthrough/amd/iommu_init.c
> +++ b/xen/drivers/passthrough/amd/iommu_init.c
> @@ -899,11 +899,8 @@ static void enable_iommu(struct amd_iommu *iommu)
>
> spin_lock_irqsave(&iommu->lock, flags);
>
> - if ( iommu->enabled )
> - {
> - spin_unlock_irqrestore(&iommu->lock, flags);
> - return;
> - }
> + if ( unlikely(iommu->enabled) )
> + goto out;
>
> amd_iommu_erratum_746_workaround(iommu);
>
> @@ -957,6 +954,8 @@ static void enable_iommu(struct amd_iommu *iommu)
> amd_iommu_flush_all_caches(iommu);
>
> iommu->enabled = 1;
> +
> + out:
> spin_unlock_irqrestore(&iommu->lock, flags);
> }
>
> @@ -966,11 +965,8 @@ static void disable_iommu(struct amd_iommu *iommu)
>
> spin_lock_irqsave(&iommu->lock, flags);
>
> - if ( !iommu->enabled )
> - {
> - spin_unlock_irqrestore(&iommu->lock, flags);
> - return;
> - }
> + if ( unlikely(!iommu->enabled) )
> + goto out;
>
> if ( !iommu->ctrl.int_cap_xt_en )
> amd_iommu_msi_enable(iommu, IOMMU_CONTROL_DISABLED);
> @@ -988,6 +984,7 @@ static void disable_iommu(struct amd_iommu *iommu)
>
> iommu->enabled = 0;
>
> + out:
> spin_unlock_irqrestore(&iommu->lock, flags);
> }
>
> --
> 2.11.0
>
--
Brian Woods
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prev parent reply other threads:[~2019-08-12 18:01 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 17:52 [Xen-devel] [PATCH] x86/AMD-Vi: Fold exit paths of {enable, disable}_iommu() Andrew Cooper
2019-08-12 18:01 ` Woods, Brian [this message]
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