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Nick Child 6511585ed6 ibmvnic: Perform tx CSO during send scrq direct 
[ Upstream commit e633e32b60 ]

During initialization with the vnic server, a bitstring is communicated
to the client regarding header info needed during CSO (See "VNIC
Capabilities" in PAPR). Most of the time, to be safe, vnic server
requests header info for CSO. When header info is needed, multiple TX
descriptors are required per skb; This limits the driver to use
send_subcrq_indirect instead of send_subcrq_direct.

Previously, the vnic server request for header info was ignored. This
allowed the use of send_sub_crq_direct. Transmissions were successful
because the bitstring returned by vnic server is broad and over
cautionary. It was observed that mlx backing devices could actually
transmit and handle CSO packets without the vnic server receiving
header info (despite the fact that the bitstring requested it).

There was a trust issue: The bitstring was overcautionary. This extra
precaution (requesting header info when the backing device may not use
it) comes at the cost of performance (using direct vs indirect hcalls
has a 30% delta in small packet RR transaction rate). So it has been
requested that the vnic server team tries to ensure that the bitstring
is more exact. In the meantime, disable CSO when it is possible to use
the skb in the send_subcrq_direct path. In other words, calculate the
checksum before handing the packet to FW when the packet is not
segmented and xmit_more is false.

Since the code path is only possible if the skb is non GSO and xmit_more
is false, the cost of doing checksum in the send_subcrq_direct path is
minimal. Any large segmented skb will have xmit_more set to true more
frequently and it is inexpensive to do checksumming on a small skb.
The worst-case workload would be a 9000 MTU TCP_RR test with close
to MTU sized packets (and TSO off). This allows xmit_more to be false
more frequently and open the code path up to use send_subcrq_direct.
Observing trace data (graph-time = 1) and packet rate with this workload
shows minimal performance degradation:

1. NIC does checksum w headers, safely use send_subcrq_indirect:
  - Packet rate: 631k txs
  - Trace data:
    ibmvnic_xmit = 44344685.87 us / 6234576 hits = AVG 7.11 us
      skb_checksum_help = 4.07 us / 2 hits = AVG 2.04 us
       ^ Notice hits, tracing this just for reassurance
      ibmvnic_tx_scrq_flush = 33040649.69 us / 5638441 hits = AVG 5.86 us
        send_subcrq_indirect = 37438922.24 us / 6030859 hits = AVG 6.21 us

2. NIC does checksum w/o headers, dangerously use send_subcrq_direct:
  - Packet rate: 831k txs
  - Trace data:
    ibmvnic_xmit = 48940092.29 us / 8187630 hits = AVG 5.98 us
      skb_checksum_help = 2.03 us / 1 hits = AVG 2.03
      ibmvnic_tx_scrq_flush = 31141879.57 us / 7948960 hits = AVG 3.92 us
        send_subcrq_indirect = 8412506.03 us / 728781 hits = AVG 11.54
         ^ notice hits is much lower b/c send_subcrq_direct was called
                                            ^ wasn't traceable

3. driver does checksum, safely use send_subcrq_direct (THIS PATCH):
  - Packet rate: 829k txs
  - Trace data:
    ibmvnic_xmit = 56696077.63 us / 8066168 hits = AVG 7.03 us
      skb_checksum_help = 8587456.16 us / 7526072 hits = AVG 1.14 us
      ibmvnic_tx_scrq_flush = 30219545.55 us / 7782409 hits = AVG 3.88 us
        send_subcrq_indirect = 8638326.44 us / 763693 hits = AVG 11.31 us

When the bitstring ever specifies that CSO does not require headers
(dependent on VIOS vnic server changes), then this patch should be
removed and replaced with one that investigates the bitstring before
using send_subcrq_direct.

Signed-off-by: Nick Child <nnac123@linux.ibm.com>
Link: https://patch.msgid.link/20240807211809.1259563-8-nnac123@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: de390657b5 ("ibmvnic: Inspect header requirements before using scrq direct")
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-03-13 12:58:20 +01:00
arch arm64: dts: rockchip: add rs485 support on uart5 of px30-ringneck-haikou 2025-03-13 12:58:20 +01:00
block partitions: mac: fix handling of bogus partition table 2025-02-21 13:57:18 +01:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto crypto: ecc - Prevent ecc_digits_from_bytes from reading too many bytes 2025-01-09 13:31:52 +01:00
Documentation x86/microcode: Prepare for minimal revision check 2025-03-07 16:45:54 +01:00
drivers ibmvnic: Perform tx CSO during send scrq direct 2025-03-13 12:58:20 +01:00
fs smb: client: fix chmod(2) regression with ATTR_READONLY 2025-03-13 12:58:20 +01:00
include rcuref: Plug slowpath race in rcuref_put() 2025-03-07 16:45:47 +01:00
init Compiler Attributes: disable __counted_by for clang < 19.1.3 2024-12-09 10:32:46 +01:00
io_uring io_uring/net: save msg_control for compat 2025-03-07 16:45:43 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-09 10:32:54 +01:00
kernel sched/core: Prevent rescheduling when interrupts are disabled 2025-03-07 16:45:48 +01:00
lib rcuref: Plug slowpath race in rcuref_put() 2025-03-07 16:45:47 +01:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm,madvise,hugetlb: check for 0-length range after end address adjustment 2025-02-27 04:10:52 -08:00
net mptcp: reset when MPTCP opts are dropped after join 2025-03-07 16:45:47 +01:00
rust rust: init: use explicit ABI to clean warning in future compilers 2025-02-17 09:40:27 +01:00
samples samples/landlock: Fix possible NULL dereference in parse_path() 2025-02-08 09:51:57 +01:00
scripts scripts/gdb: fix aarch64 userspace detection in get_current_task 2025-02-17 09:40:39 +01:00
security tomoyo: don't emit warning in tomoyo_write_control() 2025-02-17 09:40:07 +01:00
sound ALSA: hda/realtek: Fix microphone regression on ASUS N705UD 2025-03-07 16:45:45 +01:00
tools rtla/timerlat_top: Set OSNOISE_WORKLOAD for kernel threads 2025-03-07 16:45:49 +01:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt KVM: Use dedicated mutex to protect kvm_usage_count to avoid deadlock 2024-10-04 16:29:47 +02:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-04 16:29:44 +02:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -10:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS membarrier: riscv: Add full memory barrier in switch_mm() 2024-09-12 11:11:45 +02:00
Makefile Linux 6.6.82 2025-03-09 09:55:04 +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.