linux-kernel - [PATCH v3 0/2] iommu/virtio: Enable IOMMU_CAP_DERRED

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Date:   Mon, 20 Nov 2023 15:51:55 +0100
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>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Robin Murphy <robin.murphy@....com>
Cc:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        virtualization@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 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.

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

Note on testing: I tested this series on my AMD Ryzen 3900X workstation
using QEMU 8.1.2 a pass-through NVMe and Intel 82599 NIC VFs. For the
NVMe I saw an increase of about 10% in IOPS and 30% in read bandwidth
compared with v6.7-rc2. One odd thing though is that QEMU seemed to make
the entire guest resident/pinned once I passed-through a PCI device.
I seem to remember this wasn't the case with my last version but not
sure which QEMU version I used back then.

@Jean-Philippe: I didn't include your R-b's as I changed back to the
nr_endpoints check and this is like 30% of the patches.

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/

Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
---
Changes in v3:
- Removed NULL check from viommu_sync_req() (Jason)
- Went back to checking for 0 endpoints in IOTLB ops (Robin)
- Rebased on v6.7-rc2 which includes necessary iommu-dma changes
- Link to v2: https://lore.kernel.org/r/20230918-viommu-sync-map-v2-0-f33767f6cf7a@linux.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

To: Jean-Philippe Brucker <jean-philippe@...aro.org>
To: Joerg Roedel <joro@...tes.org>
To: Will Deacon <will@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
To: Robin Murphy <robin.murphy@....com>
Cc: virtualization@...ts.linux-foundation.org,
Cc: iommu@...ts.linux.dev
Cc: linux-kernel@...r.kernel.org,
Cc: Niklas Schnelle <schnelle@...ux.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 | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)
---
base-commit: 98b1cc82c4affc16f5598d4fa14b1858671b2263
change-id: 20230825-viommu-sync-map-1bf0cc4fdc15

Best regards,
-- 
Niklas Schnelle