Re: [PATCH v4 0/4] io_uring/rsrc: coalescing multi-hugepage registered buffers

[Anuj gupta <anuj1072538@gmail.com>]

On Tue, May 14, 2024 at 1:25 PM Chenliang Li <cliang01.li@samsung.com> wrote:
>
> Registered buffers are stored and processed in the form of bvec array,
> each bvec element typically points to a PAGE_SIZE page but can also work
> with hugepages. Specifically, a buffer consisting of a hugepage is
> coalesced to use only one hugepage bvec entry during registration.
> This coalescing feature helps to save both the space and DMA-mapping time.
>
> However, currently the coalescing feature doesn't work for multi-hugepage
> buffers. For a buffer with several 2M hugepages, we still split it into
> thousands of 4K page bvec entries while in fact, we can just use a
> handful of hugepage bvecs.
>
> This patch series enables coalescing registered buffers with more than
> one hugepages. It optimizes the DMA-mapping time and saves memory for
> these kind of buffers.
>
> Testing:
>
> The hugepage fixed buffer I/O can be tested using fio without
> modification. The fio command used in the following test is given
> in [1]. There's also a liburing testcase in [2]. Also, the system
> should have enough hugepages available before testing.
>
> Perf diff of 8M(4 * 2M hugepages) fio randread test:
>
> Before          After           Symbol
> .....................................................
> 4.68%                           [k] __blk_rq_map_sg
> 3.31%                           [k] dma_direct_map_sg
> 2.64%                           [k] dma_pool_alloc
> 1.09%                           [k] sg_next
>                 +0.49%          [k] dma_map_page_attrs
>
> Perf diff of 8M fio randwrite test:
>
> Before          After           Symbol
> ......................................................
> 2.82%                           [k] __blk_rq_map_sg
> 2.05%                           [k] dma_direct_map_sg
> 1.75%                           [k] dma_pool_alloc
> 0.68%                           [k] sg_next
>                 +0.08%          [k] dma_map_page_attrs
>
> First three patches prepare for adding the multi-hugepage coalescing
> into buffer registration, the 4th patch enables the feature.
>
> -----------------
> Changes since v3:
>
> - Delete unnecessary commit message
> - Update test command and test results
>
> v3 : https://lore.kernel.org/io-uring/20240514001614.566276-1-cliang01.li@samsung.com/T/#t
>
> Changes since v2:
>
> - Modify the loop iterator increment to make code cleaner
> - Minor fix to the return procedure in coalesced buffer account
> - Correct commit messages
> - Add test cases in liburing
>
> v2 : https://lore.kernel.org/io-uring/20240513020149.492727-1-cliang01.li@samsung.com/T/#t
>
> Changes since v1:
>
> - Split into 4 patches
> - Fix code style issues
> - Rearrange the change of code for cleaner look
> - Add speciallized pinned page accounting procedure for coalesced
>   buffers
> - Reordered the newly add fields in imu struct for better compaction
>
> v1 : https://lore.kernel.org/io-uring/20240506075303.25630-1-cliang01.li@samsung.com/T/#u
>
> [1]
> fio -iodepth=64 -rw=randread(-rw=randwrite) -direct=1 -ioengine=io_uring \
> -bs=8M -numjobs=1 -group_reporting -mem=shmhuge -fixedbufs -hugepage-size=2M \
> -filename=/dev/nvme0n1 -runtime=10s -name=test1
>
> [2]
> https://lore.kernel.org/io-uring/20240514051343.582556-1-cliang01.li@samsung.com/T/#u
>
> Chenliang Li (4):
>   io_uring/rsrc: add hugepage buffer coalesce helpers
>   io_uring/rsrc: store folio shift and mask into imu
>   io_uring/rsrc: add init and account functions for coalesced imus
>   io_uring/rsrc: enable multi-hugepage buffer coalescing
>
>  io_uring/rsrc.c | 217 +++++++++++++++++++++++++++++++++++++++---------
>  io_uring/rsrc.h |  12 +++
>  2 files changed, 191 insertions(+), 38 deletions(-)
>
>
> base-commit: 59b28a6e37e650c0d601ed87875b6217140cda5d
> --
> 2.34.1
>
>

I tested this series by registering multi-hugepage buffers. The coalescing helps
saving dma-mapping time. This is the gain observed on my setup, while running
the fio workload shared here.

RandomRead:
Baseline        DeltaAbs        Symbol
.....................................................
3.89%            -3.62%            [k] blk_rq_map_sg
3.58%            -3.23%            [k] dma_direct_map_sg
2.25%            -2.23%            [k] sg_next

RandomWrite:
Baseline        DeltaAbs        Symbol
.....................................................
2.46%            -2.31%            [k] dma_direct_map_sg
2.06%            -2.05%            [k] sg_next
2.08%            -1.80%            [k] blk_rq_map_sg

The liburing test case shared works fine too on my setup.

Feel free to add:
Tested-by: Anuj Gupta <anuj20.g@samsung.com>
--
Anuj Gupta