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Paolo Abeni ba27b4cdaa net: dev: introduce support for sch BYPASS for lockless qdisc 
With commit c5ad119fb6 ("net: sched: pfifo_fast use skb_array")
pfifo_fast no longer benefit from the TCQ_F_CAN_BYPASS optimization.
Due to retpolines the cost of the enqueue()/dequeue() pair has become
relevant and we observe measurable regression for the uncontended
scenario when the packet-rate is below line rate.

After commit 46b1c18f9d ("net: sched: put back q.qlen into a
single location") we can check for empty qdisc with a reasonably
fast operation even for nolock qdiscs.

This change extends TCQ_F_CAN_BYPASS support to nolock qdisc.
The new chunk of code mirrors closely the existing one for traditional
qdisc, leveraging a newly introduced helper to read atomically the
qdisc length.

Tested with pktgen in queue xmit mode, with pfifo_fast, a MQ
device, and MQ root qdisc:

threads         vanilla         patched
                kpps            kpps
1               2465            2889
2               4304            5188
4               7898            9589

Same as above, but with a single queue device:

threads         vanilla         patched
                kpps            kpps
1               2556            2827
2               2900            2900
4               5000            5000
8               4700            4700

No mesaurable changes in the contended scenarios, and more 10%
improvement in the uncontended ones.

 v1 -> v2:
  - rebased after flag name change

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Tested-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2019-03-23 21:52:36 -04:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 2019-03-16 12:20:08 -07:00
block mm: refactor readahead defines in mm.h 2019-03-12 10:04:01 -07:00
certs kexec, KEYS: Make use of platform keyring for signature verify 2019-02-04 17:34:07 -05:00
crypto lib/lzo: separate lzo-rle from lzo 2019-03-07 18:32:03 -08:00
Documentation ipv4: Allow amount of dirty memory from fib resizing to be controllable 2019-03-21 13:29:53 -07:00
drivers net: phy: Correct Cygnus/Omega PHY driver prompt 2019-03-23 20:54:18 -04:00
fs filesystem-dax for 5.1 2019-03-13 09:37:09 -07:00
include net: sched: add empty status flag for NOLOCK qdisc 2019-03-23 21:52:36 -04:00
init init/main: add checks for the return value of memblock_alloc*() 2019-03-12 10:04:02 -07:00
ipc Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 14:08:19 -07:00
kernel genetlink: make policy common to family 2019-03-22 10:38:23 -04:00
lib rhashtable: rename rht_for_each*continue as *from. 2019-03-21 14:01:10 -07:00
LICENSES LICENSES: Add GCC runtime library exception text 2019-01-16 14:54:15 -07:00
mm filemap: pass vm_fault to the mmap ra helpers 2019-03-14 14:36:20 -07:00
net net: dev: introduce support for sch BYPASS for lockless qdisc 2019-03-23 21:52:36 -04:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-03-11 08:54:01 -07:00
scripts Kconfig updates for v5.1 2019-03-13 10:06:28 -07:00
security selinux/stable-5.1 PR 20190312 2019-03-13 11:10:42 -07:00
sound Char/Misc driver patches for 5.1-rc1 2019-03-06 14:18:59 -08:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 2019-03-16 12:20:08 -07:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt ACPI updates for 5.1-rc1 2019-03-06 13:33:11 -08:00
.clang-format rhashtable: rename rht_for_each*continue as *from. 2019-03-21 14:01:10 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support for DT binding schema checks 2018-12-13 09:41:32 -06:00
.mailmap .mailmap: Add Mathieu Othacehe 2019-02-21 11:41:19 +00:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Char/Misc driver patches for 5.1-rc1 2019-03-06 14:18:59 -08:00
Kbuild Kbuild updates for v5.1 2019-03-10 17:48:21 -07:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-03-14 09:28:12 -07:00
Makefile Kbuild updates for v5.1 2019-03-10 17:48:21 -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.