mirror of
https://github.com/torvalds/linux.git
synced 2026-10-11 21:07:03 +02:00
Linux kernel source tree
fad505b2cb
Service NMI and SMI requests after PMI requests in vcpu_enter_guest() so
that KVM does not need to cancel and redo the VM-Enter if the guest
configures its PMIs to be delivered as NMIs (likely) or SMIs (unlikely).
Because APIC emulation "injects" NMIs via KVM_REQ_NMI, handling PMI
requests after NMI requests (the likely case) means KVM won't detect the
pending NMI request until the final check for outstanding requests.
Detecting requests at the final stage is costly as KVM has already loaded
guest state, potentially queued events for injection, disabled IRQs,
dropped SRCU, etc., most of which needs to be unwound.
Note that changing the order of request processing doesn't change the end
result, as KVM's final check for outstanding requests prevents entering
the guest until all requests are serviced. I.e. KVM will ultimately
coalesce events (or not) regardless of the ordering.
Using SPEC2017 benchmark programs running along with Intel vtune in a VM
demonstrates that the following code change reduces 800~1500 canceled
VM-Enters per second.
Some glory details:
Probe the invocation to vmx_cancel_injection():
$ perf probe -a vmx_cancel_injection
$ perf stat -a -e probe:vmx_cancel_injection -I 10000 # per 10 seconds
Partial results when SPEC2017 with Intel vtune are running in the VM:
On kernel without the change:
10.010018010 14254 probe:vmx_cancel_injection
20.037646388 15207 probe:vmx_cancel_injection
30.078739816 15261 probe:vmx_cancel_injection
40.114033258 15085 probe:vmx_cancel_injection
50.149297460 15112 probe:vmx_cancel_injection
60.185103088 15104 probe:vmx_cancel_injection
On kernel with the change:
10.003595390 40 probe:vmx_cancel_injection
20.017855682 31 probe:vmx_cancel_injection
30.028355883 34 probe:vmx_cancel_injection
40.038686298 31 probe:vmx_cancel_injection
50.048795162 20 probe:vmx_cancel_injection
60.069057747 19 probe:vmx_cancel_injection
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20231002040839.2630027-1-mizhang@google.com
[sean: hoist PMU/PMI above SMI too, massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.