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Jacob Keller a734c43caa ice: reduce initial wait for control queue messages 
The ice_sq_send_cmd() function is used to send messages to the control
queues used to communicate with firmware, virtual functions, and even some
hardware.

When sending a control queue message, the driver is designed to
synchronously wait for a response from the queue. Currently it waits
between checks for 100 to 150 microseconds.

Commit f86d6f9c49 ("ice: sleep, don't busy-wait, for
ICE_CTL_Q_SQ_CMD_TIMEOUT") did recently change the behavior from an
unnecessary delay into a sleep which is a significant improvement over the
old behavior of polling using udelay.

Because of the nature of PCIe transactions, the hardware won't be informed
about a new message until the write to the tail register posts. This is
only guaranteed to occur at the next register read. In ice_sq_send_cmd(),
this happens at the ice_sq_done() call. Because of this, the driver
essentially forces a minimum of one full wait time regardless of how fast
the response is.

For the hardware-based sideband queue, this is especially slow. It is
expected that the hardware will respond within 2 or 3 microseconds, an
order of magnitude faster than the 100-150 microsecond sleep.

Allow such fast completions to occur without delay by introducing a small 5
microsecond delay first before entering the sleeping timeout loop. Ensure
the tail write has been posted by using ice_flush(hw) first.

While at it, lets also remove the ICE_CTL_Q_SQ_CMD_USEC macro as it
obscures the sleep time in the inner loop. It was likely introduced to
avoid "magic numbers", but in practice sleep and delay values are easier to
read and understand when using actual numbers instead of a named constant.

This change should allow the fast hardware based control queue messages to
complete quickly without delay, while slower firmware queue response times
will sleep while waiting for the response.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Michal Schmidt <mschmidt@redhat.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
History 2023-06-22 10:23:44 -07:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2023-06-15 22:19:41 -07:00
block blk-mq: fix blk_mq_hw_ctx active request accounting 2023-06-03 17:20:00 -06:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto crypto: af_alg/hash: Fix recvmsg() after sendmsg(MSG_MORE) 2023-06-20 12:10:36 -07:00
Documentation net: ena: Fix rst format issues in readme 2023-06-21 22:43:13 -07:00
drivers ice: reduce initial wait for control queue messages 2023-06-22 10:23:44 -07:00
fs splice, net: Fix splice_to_socket() to handle pipe bufs larger than a page 2023-06-15 22:50:02 -07:00
include mptcp: introduce MPTCP_FULL_INFO getsockopt 2023-06-21 22:45:57 -07:00
init Objtool changes for v6.4: 2023-04-28 14:02:54 -07:00
io_uring Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2023-06-15 22:19:41 -07:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2023-06-15 22:19:41 -07:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2023-06-15 22:19:41 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm tcp: Use per-vma locking for receive zerocopy 2023-06-18 11:16:00 +01:00
net mptcp: pass addr to mptcp_pm_alloc_anno_list 2023-06-21 22:45:58 -07:00
rust Rust changes for v6.4 2023-04-30 11:20:22 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2023-05-25 19:57:39 -07:00
scripts bpf-next-for-netdev 2023-05-16 19:50:05 -07:00
security selinux: don't use make's grouped targets feature yet 2023-06-01 13:56:13 -04:00
sound ALSA: hda/realtek: Enable 4 amplifiers instead of 2 on a HP platform 2023-06-06 17:44:24 +02:00
tools selftests: mptcp: join: skip check if MIB counter not supported (part 2) 2023-06-21 22:45:58 -07:00
usr initramfs: Check negative timestamp to prevent broken cpio archive 2023-04-16 17:37:01 +09:00
virt KVM: Fix vcpu_array[0] races 2023-05-19 13:56:26 -04:00
.clang-format cxl for v6.4 2023-04-30 11:51:51 -07:00
.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: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore linux-kselftest-kunit-6.4-rc1 2023-04-24 12:31:32 -07:00
.mailmap mailmap: add entry for John Keeping 2023-06-12 11:31:52 -07:00
.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 MAINTAINERS: sctp: move Neil to CREDITS 2023-05-12 08:51:32 +01:00
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 tcp: Use per-vma locking for receive zerocopy 2023-06-18 11:16:00 +01:00
Makefile Linux 6.4-rc6 2023-06-11 14:35:30 -07:00
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.