[Mesa-dev] [PATCH 0/5] i965: die structs die!
kenneth at whitecape.org
Thu Jul 7 01:50:25 PDT 2011
On 07/07/2011 01:12 AM, Zou, Nanhai wrote:
> What is the intention of switching struct-style command to OUT_BATCH style?
> Zou Nanhai
1) Better code generation.
Eric has told me that GCC generates pretty sub-optimal code for
packed-bit structs, and using OUT_BATCH makes it generate more efficient
code. From what I understand, converting the larger/hotter state
packets caused a small but measurable performance difference. Though, I
doubt it matters much for these since they're rarely emitted.
Most of our newer code uses the OUT_BATCH style. I'm in favor of
picking one style and using it, not both.
3) Easy recognition of GPU commands:
Since most GPU commands are emitted via OUT_BATCH, I often used to look
for OUT_BATCH when trying and find the code that emits a particular
state packet. For the few cases that used structs, I had trouble.
4) Hardware-specific structs vs. abitrary data structures:
I also found it confusing that some structs in our driver were
descriptions of GPU commands with a specific, hardware-mandated layout,
while other structs (like brw_wm_prog_key) were just useful data
structures we invented and can change however we want. (Admittedly, we
still have some HW-specific structs, but a lot less of them.)
I'm not sure any of these are particularly compelling, but I figure we
may as well go for consistency/simplicity and drop 500 lines of unused
More information about the mesa-dev