Re: [Qemu-devel] [RESEND PATCH v6 0/3] tcg: enhance code generation quality for qemu_ld/st IRs

[Yeongkyoon Lee <yeongkyoon.lee@samsung.com>]

On 2012년 10월 20일 16:05, Yeongkyoon Lee wrote:
> Let me resend this patch, because it looks ignored except for the comment from Richard Henderson for which  I've replied.
>
> Here is the 6th version of the series optimizing TCG qemu_ld/st code generation.
>
> v6:
>    - Remove an extra argument of return addr from MMU helpers
>      Instead, embed the fast path addr to the slow path for helpers to use it
>    - Change some bitwise operations to bitfielyeongkyoonds of structure
>    - Change the name of function which handles finalization of TB code generation
>
> v5:
>    - Remove RFC tag
>
> v4:
>    - Remove CONFIG_SOFTMMU pre-condition from configure
>    - Instead, add some CONFIG_SOFTMMU condition to TCG sources
>    - Remove some unnecessary comments
>
> v3:
>    - Support CONFIG_TCG_PASS_AREG0
>      (expected to get more performance enhancement than others)
>    - Remove the configure option "--enable-ldst-optimization""
>    - Make the optimization as default on i386 and x86_64 hosts
>    - Fix some mistyping and apply checkpatch.pl before committing
>    - Test i386, arm and sparc softmmu targets on i386 and x86_64 hosts
>    - Test linux-user-test-0.3
>
> v2:
>    - Follow the submit rule of qemu
>
> v1:
>    - Initial commit request
>
> I think the generated codes from qemu_ld/st IRs are relatively heavy, which are
> up to 12 instructions for TLB hit case on i386 host.
> This patch series enhance the code quality of TCG qemu_ld/st IRs by reducing
> jump and enhancing locality.
> Main idea is simple and has been already described in the comments in
> tcg-target.c, which separates slow path (TLB miss case), and generates it at the
> end of TB.
>
> For example, the generated code from qemu_ld changes as follow.
> Before:
> (1) TLB check
> (2) If hit fall through, else jump to TLB miss case (5)
> (3) TLB hit case: Load value from host memory
> (4) Jump to next code (6)
> (5) TLB miss case: call MMU helper
> (6) ... (next code)
>
> After:
> (1) TLB check
> (2) If hit fall through, else jump to TLB miss case (5)
> (3) TLB hit case: Load value from host memory
> (4) ... (next code)
> ...
> (5) TLB miss case: call MMU helper
> (6) Jump to (8)
> (7) [embedded addr of (4)] <- never executed but read by MMU helpers
> (8) Return to next code (4)
>
> Following is some performance results measured based on qemu 1.0.
> Although there was measurement error, the results was not negligible.
>
> * EEMBC CoreMark (before -> after)
>    - Guest: i386, Linux (Tizen platform)
>    - Host: Intel Core2 Quad 2.4GHz, 2GB RAM, Linux
>    - Results: 1135.6 -> 1179.9 (+3.9%)
>
> * nbench (before -> after)
>    - Guest: i386, Linux (linux-0.2.img included in QEMU source)
>    - Host: Intel Core2 Quad 2.4GHz, 2GB RAM, Linux
>    - Results
>      . MEMORY INDEX: 1.6782 -> 1.6818 (+0.2%)
>      . INTEGER INDEX: 1.8258 -> 1.877 (+2.8%)
>      . FLOATING-POINT INDEX: 0.5944 -> 0.5954 (+0.2%)
>
> Summarized features:
>   - The changes are wrapped by macro "CONFIG_QEMU_LDST_OPTIMIZATION" and
>     they are enabled by default on i386/x86_64 hosts
>   - Forced removal of the macro will cause compilation error on i386/x86_64 hosts
>   - No implementations other than i386/x86_64 hosts yet
>
> In addition, I have tried to remove the generated codes of calling MMU helpers
> for TLB miss case from end of TB, however, have not found good solution yet.
> In my opinion, TLB hit case performance could be degraded if removing the
> calling codes, because it needs to set runtime parameters, such as, data,
> mmu index and return address, in register or stack though they are not used
> in TLB hit case.
> This remains as a further issue.
>
> Yeongkyoon Lee (3):
>    configure: Add CONFIG_QEMU_LDST_OPTIMIZATION for TCG qemu_ld/st
>      optimization
>    tcg: Add extended GETPC mechanism for MMU helpers with ldst
>      optimization
>    tcg: Optimize qemu_ld/st by generating slow paths at the end of a
>      block
>
>   configure             |    6 +
>   exec-all.h            |   36 +++++
>   exec.c                |   11 ++
>   softmmu_template.h    |   16 +-
>   tcg/i386/tcg-target.c |  415 +++++++++++++++++++++++++++++++++----------------
>   tcg/tcg.c             |   12 ++
>   tcg/tcg.h             |   30 ++++
>   7 files changed, 385 insertions(+), 141 deletions(-)
>
> --
> 1.7.5.4
>

Ping?