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Linux kernel for uConsole
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Wanpeng Li e409b81d9d Revert "locking/pvqspinlock: Don't wait if vCPU is preempted" 
commit 89340d0935 upstream.

This patch reverts commit 75437bb304 (locking/pvqspinlock: Don't
wait if vCPU is preempted).  A large performance regression was caused
by this commit.  on over-subscription scenarios.

The test was run on a Xeon Skylake box, 2 sockets, 40 cores, 80 threads,
with three VMs of 80 vCPUs each.  The score of ebizzy -M is reduced from
13000-14000 records/s to 1700-1800 records/s:

          Host                Guest                score

vanilla w/o kvm optimizations     upstream    1700-1800 records/s
vanilla w/o kvm optimizations     revert      13000-14000 records/s
vanilla w/ kvm optimizations      upstream    4500-5000 records/s
vanilla w/ kvm optimizations      revert      14000-15500 records/s

Exit from aggressive wait-early mechanism can result in premature yield
and extra scheduling latency.

Actually, only 6% of wait_early events are caused by vcpu_is_preempted()
being true.  However, when one vCPU voluntarily releases its vCPU, all
the subsequently waiters in the queue will do the same and the cascading
effect leads to bad performance.

kvm optimizations:
[1] commit d73eb57b80 (KVM: Boost vCPUs that are delivering interrupts)
[2] commit 266e85a5ec (KVM: X86: Boost queue head vCPU to mitigate lock waiter preemption)

Tested-by: loobinliu@tencent.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: loobinliu@tencent.com
Cc: stable@vger.kernel.org
Fixes: 75437bb304 (locking/pvqspinlock: Don't wait if vCPU is preempted)
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-10-11 18:21:06 +02:00
arch MIPS: Treat Loongson Extensions as ASEs 2019-10-11 18:20:55 +02:00
block block: mq-deadline: Fix queue restart handling 2019-10-07 18:57:19 +02:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: skcipher - Unmap pages after an external error 2019-10-11 18:20:52 +02:00
Documentation ovl: fix regression caused by overlapping layers detection 2019-09-21 07:17:14 +02:00
drivers mmc: sdhci-of-esdhc: set DMA snooping based on DMA coherence 2019-10-11 18:21:05 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs 9p/cache.c: Fix memory leak in v9fs_cache_session_get_cookie 2019-10-07 18:57:29 +02:00
include ASoC: Define a set of DAPM pre/post-up events 2019-10-11 18:20:47 +02:00
init initramfs: don't free a non-existent initrd 2019-10-01 08:26:09 +02:00
ipc ipc/mqueue.c: only perform resource calculation if user valid 2019-08-06 19:06:52 +02:00
kernel Revert "locking/pvqspinlock: Don't wait if vCPU is preempted" 2019-10-11 18:21:06 +02:00
lib kmemleak: increase DEBUG_KMEMLEAK_EARLY_LOG_SIZE default to 16K 2019-10-07 18:57:17 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm usercopy: Avoid HIGHMEM pfn warning 2019-10-11 18:20:58 +02:00
net NFC: fix attrs checks in netlink interface 2019-10-07 18:57:28 +02:00
samples samples, bpf: suppress compiler warning 2019-07-14 08:11:04 +02:00
scripts randstruct: Check member structs in is_pure_ops_struct() 2019-10-05 13:10:02 +02:00
security smack: use GFP_NOFS while holding inode_smack::smk_lock 2019-10-07 18:57:27 +02:00
sound ASoC: sgtl5000: Improve VAG power and mute control 2019-10-11 18:20:47 +02:00
tools perf stat: Fix a segmentation fault when using repeat forever 2019-10-11 18:21:01 +02:00
usr kbuild: clean compressed initramfs image 2019-10-07 18:57:16 +02:00
virt KVM: coalesced_mmio: add bounds checking 2019-09-21 07:16:44 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS platform/x86: Add Intel AtomISP2 dummy / power-management driver 2019-04-20 09:16:02 +02:00
Makefile Linux 4.19.78 2019-10-07 18:57:29 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.