From: David Gibson <david@gibson.dropbear.id.au>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [PATCH kernel] vfio/spapr: Add cond_resched() for huge updates
Date: Sat, 23 Sep 2017 13:58:36 +1000 [thread overview]
Message-ID: <20170923035836.GV4998@umbus.fritz.box> (raw)
In-Reply-To: <20170921100024.44924-1-aik@ozlabs.ru>
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On Thu, Sep 21, 2017 at 08:00:24PM +1000, Alexey Kardashevskiy wrote:
> Clearing very big IOMMU tables can trigger soft lockups. This adds
> cond_resched() for every million TCE updates.
>
> The testcase is POWER9 box with 264GB guest, 4 VFIO devices from
> independent IOMMU groups, 64K IOMMU pages. This configuration produces
> 4325376 TCE entries, each entry update incurs 4 OPAL calls to update
> an individual PE TCE cache. Reducing table size to 4194304 (i.e. 256GB
> guest) or removing one of 4 VFIO devices makes the problem go away so
> doing cond_resched() after every million TCE updates seems sufficient.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> drivers/vfio/vfio_iommu_spapr_tce.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 63112c36ab2d..be3839ea3150 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -502,11 +502,15 @@ static int tce_iommu_clear(struct tce_container *container,
> struct iommu_table *tbl,
> unsigned long entry, unsigned long pages)
> {
> - unsigned long oldhpa;
> + unsigned long oldhpa, n;
> long ret;
> enum dma_data_direction direction;
>
> - for ( ; pages; --pages, ++entry) {
> + for (n = 0; pages; --pages, ++entry, ++n) {
> +
> + if (n && (n % 1000000 == 0))
> + cond_resched();
> +
> direction = DMA_NONE;
> oldhpa = 0;
> ret = iommu_tce_xchg(tbl, entry, &oldhpa, &direction);
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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WARNING: multiple messages have this Message-ID (diff)
From: David Gibson <david@gibson.dropbear.id.au>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [PATCH kernel] vfio/spapr: Add cond_resched() for huge updates
Date: Sat, 23 Sep 2017 03:58:36 +0000 [thread overview]
Message-ID: <20170923035836.GV4998@umbus.fritz.box> (raw)
In-Reply-To: <20170921100024.44924-1-aik@ozlabs.ru>
[-- Attachment #1: Type: text/plain, Size: 1835 bytes --]
On Thu, Sep 21, 2017 at 08:00:24PM +1000, Alexey Kardashevskiy wrote:
> Clearing very big IOMMU tables can trigger soft lockups. This adds
> cond_resched() for every million TCE updates.
>
> The testcase is POWER9 box with 264GB guest, 4 VFIO devices from
> independent IOMMU groups, 64K IOMMU pages. This configuration produces
> 4325376 TCE entries, each entry update incurs 4 OPAL calls to update
> an individual PE TCE cache. Reducing table size to 4194304 (i.e. 256GB
> guest) or removing one of 4 VFIO devices makes the problem go away so
> doing cond_resched() after every million TCE updates seems sufficient.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> drivers/vfio/vfio_iommu_spapr_tce.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 63112c36ab2d..be3839ea3150 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -502,11 +502,15 @@ static int tce_iommu_clear(struct tce_container *container,
> struct iommu_table *tbl,
> unsigned long entry, unsigned long pages)
> {
> - unsigned long oldhpa;
> + unsigned long oldhpa, n;
> long ret;
> enum dma_data_direction direction;
>
> - for ( ; pages; --pages, ++entry) {
> + for (n = 0; pages; --pages, ++entry, ++n) {
> +
> + if (n && (n % 1000000 == 0))
> + cond_resched();
> +
> direction = DMA_NONE;
> oldhpa = 0;
> ret = iommu_tce_xchg(tbl, entry, &oldhpa, &direction);
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2017-09-23 5:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-21 10:00 [PATCH kernel] vfio/spapr: Add cond_resched() for huge updates Alexey Kardashevskiy
2017-09-21 10:00 ` Alexey Kardashevskiy
2017-09-23 3:58 ` David Gibson [this message]
2017-09-23 3:58 ` David Gibson
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