Bug 24981

Summary:	commit 'i965: Fix BRW_WM_MAX_INSN to reflect current limits.' causes performance regressions
Product:	Mesa	Reporter:	maximlevitsky
Component:	Drivers/DRI/i965	Assignee:	Eric Anholt <eric>
Status:	RESOLVED FIXED	QA Contact:
Severity:	major
Priority:	high	CC:	eric, shuang.he
Version:	git	Keywords:	regression
Hardware:	Other
OS:	All
Whiteboard:
i915 platform:		i915 features:

Description maximlevitsky 2009-11-07 11:59:07 UTC

I bisected this commit.

2c30ee9bd69ed606b984c051748a7cdb34905eeb is first bad commit
commit 2c30ee9bd69ed606b984c051748a7cdb34905eeb
Author: Eric Anholt <eric@anholt.net>
Date:   Fri Oct 30 13:20:13 2009 -0700

    i965: Fix BRW_WM_MAX_INSN to reflect current limits.
    
    Part of fixing bug #24355.



To reproduce, just start the sauerbraten game.
I play now the version in ubuntu 9.10 (0.0.20090504.dfsg-1)

I tested the 'Private stan sauer', part 2 (run and guns ||)
Here attached version of configuration I used.

With this regression, I see frequent hick-ups, that make the game almost
unplayable. 


Without the regression I get about 18-24 FPS.


I bisected this bug (and tested successfully master branch with this
commit reverted)

Comment 1 Gordon Jin 2009-11-08 17:31:51 UTC

(moving to mesa category)

This seems similar to bug#24847

Comment 2 Eric Anholt 2009-11-10 16:06:34 UTC

Thanks for the bisect -- I had a hard time believing it caused a regression, but sure enough:

commit c5413839b3e99c7b162f1260142f3c175502b0ce
Author: Eric Anholt <eric@anholt.net>
Date:   Tue Nov 10 15:51:29 2009 -0800

    i965: avoid memsetting all the BRW_WM_MAX_INSN arrays for every compile.
    
    For an app that's blowing out the state cache, like sauerbraten, the
    memset of the giant arrays ended up taking 11% of the CPU even when only a
    "few" of the entries got used.  With this, the WM program compile drops back
    down to 1% of CPU time.
    
    Bug #24981 (bisected to BRW_WM_MAX_INSN increase).

Of course, the real problem here is that sauer's blowing out the state cache.

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