linux-kernel - [PATCH v2 0/2] iommu/virtio: Enable IOMMU_CAP_DERRED

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Date:   Mon, 18 Sep 2023 13:51:42 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>
Cc:     virtualization@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Niklas Schnelle <schnelle@...ux.ibm.com>
Subject: [PATCH v2 0/2] iommu/virtio: Enable IOMMU_CAP_DERRED_FLUSH

Hi All,

Previously I used virtio-iommu as a non-s390x test vehicle[0] for the
single queue flushing scheme introduced by my s390x DMA API conversion
series[1]. For this I modified virtio-iommu to a) use .iotlb_sync_map
and b) enable IOMMU_CAP_DEFERRED_FLUSH. It turned out that deferred
flush and even just the introduction of ops->iotlb_sync_map yield
performance uplift[2] even with per-CPU queues. So here is a small
series of these two changes. This still applies on top of my series[1]
because its first patch titled "iommu: Allow .iotlb_sync_map to fail and
handle s390's -ENOMEM return" enable ops->iotlb_sync_map to return
errors and virtio-iommu's sync can fail. This also makes sure there is
no merge conflict with that series.

The code is also available on the b4/viommu-deferred-flush branch of my
kernel.org git repository[3]

Thanks,
Niklas

[0] https://lore.kernel.org/lkml/20230726111433.1105665-1-schnelle@linux.ibm.com/
[1] https://lore.kernel.org/lkml/20230825-dma_iommu-v12-0-4134455994a7@linux.ibm.com/
[2] https://lore.kernel.org/lkml/20230802123612.GA6142@myrica/
[3] https://git.kernel.org/pub/scm/linux/kernel/git/niks/linux.git/log/?h=b4/viommu-deferred-flush

Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
---
Changes in v2:
- Check for viommu == NULL in viommu_sync_req() instead of for
  0 endpoints in ops (Jean-Philippe)
- Added comment where viommu can be NULL (me)
- Link to v1: https://lore.kernel.org/r/20230825-viommu-sync-map-v1-0-56bdcfaa29ec@linux.ibm.com

---
Niklas Schnelle (2):
      iommu/virtio: Make use of ops->iotlb_sync_map
      iommu/virtio: Add ops->flush_iotlb_all and enable deferred flush

 drivers/iommu/virtio-iommu.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)
---
base-commit: e165388f6d32dc8a49f49ef6e80584ad3def3d78
change-id: 20230825-viommu-sync-map-1bf0cc4fdc15

Best regards,
-- 
Niklas Schnelle
Linux on Z Development

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