RE: [patches] Possible PowerPC LIBC optimization

["Nitin Gupta" <ngupta@xxxxxxxxxx>]

Hello Mark/Conn,

Could you please send pointer to glibc thread about discussion of this
patch?

Regards,
Nitin
-----Original Message-----
From: Mark Hatle [mailto:mark.hatle@xxxxxxxxxxxxx] 
Sent: Tuesday, May 15, 2007 10:02 AM
To: patches@xxxxxxxxxx
Cc: Conn Clark
Subject: [patches] Possible PowerPC LIBC optimization

In the PowerPC community Conn Clark has been doing some interesting
optimization work in glibc.  Much of it however, doesn't seem to be
acceptable to the mainline glibc due to being very processor and
architecture specific.

The following information describes a simple change that made a large
performance improvement on the PPC 750 processor, and is believed will
make similar improvements on other PowerPC that contain the dcbt
instruction.

From Conn Clark:
> To see where I made the changes just search for "dcbt". The first two
> dcbt's in the functions _int_malloc and _int_free are the ones that
> make the biggest difference. The rest seem to help but they fall
> withing the noise margin of my test(a compile of glibc ).

Attached is the patch that Clark sent me against glibc-2.5.  I don't
think it is directly applicable as stated to glibc, however the idea
behind it appears to be sound.

There are point in the malloc/free that preloading the cache (at least
on PPC) makes sense.  So adding hooks in these locations may allow us to
configure in processor specific items that could dramatically improve
the performance on various processors.

--Mark