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Re: [PATCH] Avoid unnecessary busy loop in __lll_timedlock_wait on ARM.
- From: David Miller <davem at davemloft dot net>
- To: carlos at systemhalted dot org
- Cc: drow at false dot org, joseph at codesourcery dot com, schwab at linux-m68k dot org, thomas_schwinge at mentor dot com, kkojima at rr dot iij4u dot or dot jp, marcus dot shawcroft at linaro dot org, katsuki dot uwatoko at toshiba dot co dot jp, libc-ports at sourceware dot org
- Date: Sat, 09 Feb 2013 01:49:09 -0500 (EST)
- Subject: Re: [PATCH] Avoid unnecessary busy loop in __lll_timedlock_wait on ARM.
- References: <F3B6523425E7914AA6214ED358D820AF25D90F5D@TGXML316.toshiba.local> <Pine.LNX.4.64.1302072328580.17419@digraph.polyomino.org.uk> <CAE2sS1isYziYbmy1sgvhVPTp8_3hbNYKsnj_pXrZmjv53=mm6Q@mail.gmail.com>
From: "Carlos O'Donell" <carlos@systemhalted.org>
Date: Fri, 8 Feb 2013 23:18:42 -0500
> I see that sparc32 also has a unique copy of lowlevellock.c Why the
> use of *_24_* atomic primitives? Faster?
On pre-v9 32-bit sparc, we lack any usable atomic compare and
swap.
All we have is an 8-bit spinlock.
So we implement things in a 32-bit word which is composed of a 24-bit
counter and an 8-bit lock.