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Chuck Lever 85f795b98f svcrdma: Reduce the number of rdma_rw contexts per-QP 
[ Upstream commit 5924331589 ]

There is an upper bound on the number of rdma_rw contexts that can
be created per QP.

This invisible upper bound is because rdma_create_qp() adds one or
more additional SQEs for each ctxt that the ULP requests via
qp_attr.cap.max_rdma_ctxs. The QP's actual Send Queue length is on
the order of the sum of qp_attr.cap.max_send_wr and a factor times
qp_attr.cap.max_rdma_ctxs. The factor can be up to three, depending
on whether MR operations are required before RDMA Reads.

This limit is not visible to RDMA consumers via dev->attrs. When the
limit is surpassed, QP creation fails with -ENOMEM. For example:

svcrdma's estimate of the number of rdma_rw contexts it needs is
three times the number of pages in RPCSVC_MAXPAGES. When MAXPAGES
is about 260, the internally-computed SQ length should be:

64 credits + 10 backlog + 3 * (3 * 260) = 2414

Which is well below the advertised qp_max_wr of 32768.

If RPCSVC_MAXPAGES is increased to 4MB, that's 1040 pages:

64 credits + 10 backlog + 3 * (3 * 1040) = 9434

However, QP creation fails. Dynamic printk for mlx5 shows:

calc_sq_size:618:(pid 1514): send queue size (9326 * 256 / 64 -> 65536) exceeds limits(32768)

Although 9326 is still far below qp_max_wr, QP creation still
fails.

Because the total SQ length calculation is opaque to RDMA consumers,
there doesn't seem to be much that can be done about this except for
consumers to try to keep the requested rdma_rw ctxt count low.

Fixes: 2da0f610e7 ("svcrdma: Increase the per-transport rw_ctx count")
Reviewed-by: NeilBrown <neil@brown.name>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Stable-dep-of: afcae7d7b8 ("RDMA/core: add rdma_rw_max_sge() helper for SQ sizing")
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-03-04 07:19:43 -05:00
arch arm64: dts: qcom: sdm845-db845c: specify power for WiFi CH1 2026-03-04 07:19:30 -05:00
block block,bfq: fix aux stat accumulation destination 2026-02-11 13:35:29 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-02-06 16:41:53 +01:00
Documentation PCI: endpoint: Automatically create a function specific attributes group 2026-02-19 16:21:46 +01:00
drivers RDMA/core: Fix a couple of obvious typos in comments 2026-03-04 07:19:42 -05:00
fs procfs: fix missing RCU protection when reading real_parent in do_task_stat() 2026-03-04 07:19:37 -05:00
include RDMA/core: Fix a couple of obvious typos in comments 2026-03-04 07:19:42 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:21:45 +02:00
io_uring io_uring: fix filename leak in __io_openat_prep() 2026-01-19 13:09:54 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:05:26 +01:00
kernel timers: Replace in_irq() with in_hardirq() 2026-03-04 07:19:36 -05:00
lib lib/crypto: aes: Fix missing MMU protection for AES S-box 2026-01-19 13:10:13 +01:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/kfence: randomize the freelist on initialization 2026-02-11 13:35:27 +01:00
net
samples samples: mei: Fix building on musl libc 2025-08-28 16:24:07 +02:00
scripts kbuild: Use CRC32 and a 1MiB dictionary for XZ compressed modules 2026-01-19 13:10:05 +01:00
security smack: /smack/doi: accept previously used values 2026-03-04 07:19:31 -05:00
sound ASoC: fsl_xcvr: fix missing lock in fsl_xcvr_mode_put() 2026-02-19 16:21:44 +01:00
tools spi: tools: Add include folder to .gitignore 2026-03-04 07:19:32 -05:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:05:22 +01:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-02-11 13:35:27 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:09:36 +09:00
Makefile Linux 5.15.201 2026-02-19 16:21:47 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.