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arm/kvm: Enable support for KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE

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Now that we have Eager Page Split support added for ARM in the kernel,
enable it in Qemu. This adds,
 -eager-split-size to -accel sub-options to set the eager page split chunk size.
 -enable KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE.

The chunk size specifies how many pages to break at a time, using a
single allocation. Bigger the chunk size, more pages need to be
allocated ahead of time.

Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Message-id: 20230905091246.1931-1-shameerali.kolothum.thodi@huawei.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Shameer Kolothum
2023-09-05 10:12:46 +01:00
committed by Peter Maydell
parent d03396a8bb
commit c8f2eb5d41
4 changed files with 78 additions and 0 deletions
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15
qemu-options.hx
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@@ -186,6 +186,7 @@ DEF("accel", HAS_ARG, QEMU_OPTION_accel,
" split-wx=on|off (enable TCG split w^x mapping)\n"
" tb-size=n (TCG translation block cache size)\n"
" dirty-ring-size=n (KVM dirty ring GFN count, default 0)\n"
" eager-split-size=n (KVM Eager Page Split chunk size, default 0, disabled. ARM only)\n"
" notify-vmexit=run|internal-error|disable,notify-window=n (enable notify VM exit and set notify window, x86 only)\n"
" thread=single|multi (enable multi-threaded TCG)\n", QEMU_ARCH_ALL)
SRST
@@ -244,6 +245,20 @@ SRST
is disabled (dirty-ring-size=0). When enabled, KVM will instead
record dirty pages in a bitmap.
``eager-split-size=n``
KVM implements dirty page logging at the PAGE_SIZE granularity and
enabling dirty-logging on a huge-page requires breaking it into
PAGE_SIZE pages in the first place. KVM on ARM does this splitting
lazily by default. There are performance benefits in doing huge-page
split eagerly, especially in situations where TLBI costs associated
with break-before-make sequences are considerable and also if guest
workloads are read intensive. The size here specifies how many pages
to break at a time and needs to be a valid block size which is
1GB/2MB/4KB, 32MB/16KB and 512MB/64KB for 4KB/16KB/64KB PAGE_SIZE
respectively. Be wary of specifying a higher size as it will have an
impact on the memory. By default, this feature is disabled
(eager-split-size=0).
``notify-vmexit=run|internal-error|disable,notify-window=n``
Enables or disables notify VM exit support on x86 host and specify
the corresponding notify window to trigger the VM exit if enabled.