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Re: [Qemu-devel] [PATCH v3 00/10] migration: improve and cleanup compres
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v3 00/10] migration: improve and cleanup compression |
Date: |
Wed, 25 Apr 2018 18:04:44 +0100 |
User-agent: |
Mutt/1.9.5 (2018-04-13) |
* address@hidden (address@hidden) wrote:
> From: Xiao Guangrong <address@hidden>
>
Queued.
> Changelog in v3:
> Following changes are from Peter's review:
> 1) use comp_param[i].file and decomp_param[i].compbuf to indicate if
> the thread is properly init'd or not
> 2) save the file which is used by ram loader to the global variable
> instead it is cached per decompression thread
>
> Changelog in v2:
> Thanks to the review from Dave, Peter, Wei and Jiang Biao, the changes
> in this version are:
> 1) include the performance number in the cover letter
> 2)add some comments to explain how to use z_stream->opaque in the
> patchset
> 3) allocate a internal buffer for per thread to store the data to
> be compressed
> 4) add a new patch that moves some code to ram_save_host_page() so
> that 'goto' can be omitted gracefully
> 5) split the optimization of compression and decompress into two
> separated patches
> 6) refine and correct code styles
>
>
> This is the first part of our work to improve compression to make it
> be more useful in the production.
>
> The first patch resolves the problem that the migration thread spends
> too much CPU resource to compression memory if it jumps to a new block
> that causes the network is used very deficient.
>
> The second patch fixes the performance issue that too many VM-exits
> happen during live migration if compression is being used, it is caused
> by huge memory returned to kernel frequently as the memory is allocated
> and freed for every signal call to compress2()
>
> The remaining patches clean the code up dramatically
>
> Performance numbers:
> We have tested it on my desktop, i7-4790 + 16G, by locally live migrate
> the VM which has 8 vCPUs + 6G memory and the max-bandwidth is limited to
> 350. During the migration, a workload which has 8 threads repeatedly
> written total 6G memory in the VM.
>
> Before this patchset, its bandwidth is ~25 mbps, after applying, the
> bandwidth is ~50 mbp.
>
> We also collected the perf data for patch 2 and 3 on our production,
> before the patchset:
> + 57.88% kqemu [kernel.kallsyms] [k] queued_spin_lock_slowpath
> + 10.55% kqemu [kernel.kallsyms] [k] __lock_acquire
> + 4.83% kqemu [kernel.kallsyms] [k] flush_tlb_func_common
>
> - 1.16% kqemu [kernel.kallsyms] [k] lock_acquire
> ▒
> - lock_acquire
> ▒
> - 15.68% _raw_spin_lock
> ▒
> + 29.42% __schedule
> ▒
> + 29.14% perf_event_context_sched_out
> ▒
> + 23.60% tdp_page_fault
> ▒
> + 10.54% do_anonymous_page
> ▒
> + 2.07% kvm_mmu_notifier_invalidate_range_start
> ▒
> + 1.83% zap_pte_range
> ▒
> + 1.44% kvm_mmu_notifier_invalidate_range_end
>
>
> apply our work:
> + 51.92% kqemu [kernel.kallsyms] [k] queued_spin_lock_slowpath
> + 14.82% kqemu [kernel.kallsyms] [k] __lock_acquire
> + 1.47% kqemu [kernel.kallsyms] [k] mark_lock.clone.0
> + 1.46% kqemu [kernel.kallsyms] [k] native_sched_clock
> + 1.31% kqemu [kernel.kallsyms] [k] lock_acquire
> + 1.24% kqemu libc-2.12.so [.] __memset_sse2
>
> - 14.82% kqemu [kernel.kallsyms] [k] __lock_acquire
> ▒
> - __lock_acquire
> ▒
> - 99.75% lock_acquire
> ▒
> - 18.38% _raw_spin_lock
> ▒
> + 39.62% tdp_page_fault
> ▒
> + 31.32% __schedule
> ▒
> + 27.53% perf_event_context_sched_out
> ▒
> + 0.58% hrtimer_interrupt
>
>
> We can see the TLB flush and mmu-lock contention have gone.
>
> Xiao Guangrong (10):
> migration: stop compressing page in migration thread
> migration: stop compression to allocate and free memory frequently
> migration: stop decompression to allocate and free memory frequently
> migration: detect compression and decompression errors
> migration: introduce control_save_page()
> migration: move some code to ram_save_host_page
> migration: move calling control_save_page to the common place
> migration: move calling save_zero_page to the common place
> migration: introduce save_normal_page()
> migration: remove ram_save_compressed_page()
>
> migration/qemu-file.c | 43 ++++-
> migration/qemu-file.h | 6 +-
> migration/ram.c | 482
> ++++++++++++++++++++++++++++++--------------------
> 3 files changed, 324 insertions(+), 207 deletions(-)
>
> --
> 2.14.3
>
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK