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Re: [Qemu-devel] Hack integrating SeaBios / LinuxBoot option rom with QE


From: Avi Kivity
Subject: Re: [Qemu-devel] Hack integrating SeaBios / LinuxBoot option rom with QEMU trace backends
Date: Tue, 11 Oct 2011 11:35:15 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0) Gecko/20110927 Thunderbird/7.0

On 10/11/2011 11:18 AM, Daniel P. Berrange wrote:
>
>  The rep/ins implementation is still slow, optimizing it can help.
>
>  What does 'perf top' say when running this workload?

To ensure it only recorded the LinuxBoot code, I created a 100 MB
kernel image which takes approx 30 seconds to copy. Here is the
perf output for approx 15 seconds of that copy:

              1906.00 15.0% read_hpet                       [kernel]

Recent kernels are very clock intensive...

              1029.00  8.1% x86_emulate_insn                [kvm]
               863.00  6.8% test_cc                         [kvm]

test_cc() is wierd - not called on this path at all.

               661.00  5.2% emulator_get_segment            [kvm]
               631.00  5.0% kvm_mmu_pte_write               [kvm]
               535.00  4.2% __linearize                     [kvm]
               431.00  3.4% do_raw_spin_lock                [kernel]
               356.00  2.8% vmx_get_segment                 [kvm_intel]
               330.00  2.6% vmx_segment_cache_test_set      [kvm_intel]
               308.00  2.4% segmented_write                 [kvm]
               291.00  2.3% vread_hpet                      [kernel].vsyscall_fn
               251.00  2.0% vmx_get_cpl                     [kvm_intel]
               230.00  1.8% trace_kvm_mmu_audit             [kvm]
               207.00  1.6% kvm_write_guest                 [kvm]
               199.00  1.6% emulator_write_emulated         [kvm]
               187.00  1.5% emulator_write_emulated_onepage [kvm]
               185.00  1.5% kvm_write_guest_page            [kvm]
               177.00  1.4% vmx_get_segment_base            [kvm_intel]
               158.00  1.2% fw_cfg_io_readb                 qemu-system-x86_64

This is where something gets done.

               148.00  1.2% register_address_increment      [kvm]
               142.00  1.1% emulator_write_phys             [kvm]

And here too. So 97.7% overhead, which could be reduced by a factor of 4096 if the code is made more rep-aware.



--
error compiling committee.c: too many arguments to function




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