From: David Mosberger-Tang <davidm@hpl.hp.com>
Date: Thu, 28 Apr 2005 04:19:04 +0000 (-0700)
Subject: [IA64] Reschedule break_fault() for better performance.
X-Git-Tag: v2.6.13-rc2~59^2~14^2~9
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f8fa5448fc9b4a7806b1297a0b57808f12fe4d43;p=pandora-kernel.git

[IA64] Reschedule break_fault() for better performance.

This patch reorganizes break_fault() to optimistically assume that a
system-call is being performed from user-space (which is almost always
the case).  If it turns out that (a) we're not being called due to a
system call or (b) we're being called from within the kernel, we fixup
the no-longer-valid assumptions in non_syscall() and .break_fixup(),
respectively.

With this approach, there are 3 major phases:

 - Phase 1: Read various control & application registers, in
	    particular the current task pointer from AR.K6.
 - Phase 2: Do all memory loads (load system-call entry,
	    load current_thread_info()->flags, prefetch
	    kernel register-backing store) and switch
	    to kernel register-stack.
 - Phase 3: Call ia64_syscall_setup() and invoke
	    syscall-handler.

Good for 26-30 cycles of improvement on break-based syscall-path.

Signed-off-by: David Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
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