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Chris Wilson 17db337f50 drm/i915: Truly bump ready tasks ahead of busywaits 
In commit b7404c7ecb ("drm/i915: Bump ready tasks ahead of
busywaits"), I tried cutting a corner in order to not install a signal
for each of our dependencies, and only listened to requests on which we
were intending to busywait. The compromise that was made was that
instead of then being able to promote the request with a full
NOSEMAPHORE like its non-busywaiting brethren, as we had not ensured we
had cleared the semaphore chain, we settled for only using the NEWCLIENT
boost. With an over saturated system with multiple NEWCLIENTS in flight
at any time, this was found to be an inadequate promotion and left us
with a much poorer scheduling order than prior to using semaphores.

The outcome of this patch, is that all requests have NOSEMAPHORE
priority when they have no dependencies and are ready to run and not
busywait, restoring the pre-semaphore ordering on saturated systems.

We can demonstrate the effect of poor scheduling order by oversaturating
the system using gem_wsim on a system with multiple vcs engines
(i.e running the same workloads across more clients than required for
peak throughput, e.g. media_load_balance_17i7.wsim -c4 -b context):

x v5.1 (normalized)
+ tip
* fix
+------------------------------------------------------------------------+
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+------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x 120       0.99456       1.00628      0.999985     1.0001545  0.0024387139
+ 120      0.873021       1.00037      0.884134    0.90148752   0.039190862
Difference at 99.5% confidence
	-0.098667 +/- 0.0110762
	-9.86517% +/- 1.10745%
	(Student's t, pooled s = 0.0277657)
% 120      0.990207       1.00165     0.9970265    0.99699748     0.0021024
Difference at 99.5% confidence
	-0.003157 +/- 0.000908245
	-0.315651% +/- 0.0908105%
	(Student's t, pooled s = 0.00227678)

Fixes: b7404c7ecb ("drm/i915: Bump ready tasks ahead of busywaits")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
Cc: Dmitry Ermilov <dmitry.ermilov@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190515130052.4475-2-chris@chris-wilson.co.uk
 		2019-05-17 13:56:13 +01:00
Documentation drm: revocation check at drm subsystem 2019-05-09 09:44:41 +02:00
LICENSES LICENSES: Add GCC runtime library exception text 2019-01-16 14:54:15 -07:00
arch Merge tag 'drm-intel-next-2019-04-17' of git://anongit.freedesktop.org/drm/drm-intel into drm-next 2019-04-24 10:02:20 +10:00
block block: do not leak memory in bio_copy_user_iov() 2019-04-10 16:14:40 -06:00
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
drivers drm/i915: Truly bump ready tasks ahead of busywaits 2019-05-17 13:56:13 +01:00
fs Merge branch 'page-refs' (page ref overflow) 2019-04-14 15:09:40 -07:00
include drm/i915/icl: More workaround for port F detection due to broken VBTs 2019-05-14 13:46:59 +03:00
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 Merge branch 'page-refs' (page ref overflow) 2019-04-14 15:09:40 -07:00
lib Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-04-09 16:20:59 -10:00
mm Merge branch 'page-refs' (page ref overflow) 2019-04-14 15:09:40 -07:00
net Revert "SUNRPC: Micro-optimise when the task is known not to be sleeping" 2019-04-11 15:41:14 -04:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-03-11 08:54:01 -07:00
scripts fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock 2019-04-06 07:01:55 -10:00
security apparmor: Restore Y/N in /sys for apparmor's "enabled" 2019-04-10 04:24:48 -07:00
sound Linux 5.1-rc5 2019-04-15 15:51:49 +10:00
tools for-linus-20190412 2019-04-13 16:23:16 -07:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt KVM/ARM fixes for 5.1 2019-03-28 19:07:30 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-04-12 12:49:54 +02:00
.cocciconfig
…
.get_maintainer.ignore
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.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 Update Nicolas Pitre's email address 2019-04-02 18:12:44 -10:00
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 drm-misc-next for v5.2: 2019-04-24 10:12:50 +10:00
Makefile Linux 5.1-rc5 2019-04-14 15:17:41 -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.