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[IA64] On return from syscall, hint b7 with __kernel_syscall_via_epc().

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Why is this a good idea?  Clearing b7 to 0 is guaranteed to do us no
good and writing it with __kernel_syscall_via_epc() yields a 6 cycle
improvement _if_ the application performs another EPC-based system-
call without overwriting b7, which is not all that uncommon.  Well
worth the minimal cost of 1 bundle of code.

Signed-off-by: David Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
David Mosberger-Tang 2005-04-27 21:16:07 -07:00 committed by Tony Luck
parent 3c79c8b1d9
commit 96e017495e
1 changed files with 8 additions and 1 deletions
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9
arch/ia64/kernel/entry.S
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@ -692,7 +692,7 @@ ENTRY(ia64_leave_syscall)
;;
(p6) ld4 r31=[r18] // load current_thread_info()->flags
ld8 r19=[r2],PT(B6)-PT(LOADRS) // load ar.rsc value for "loadrs"
mov b7=r0 // clear b7
nop.i 0
;;
ld8 r23=[r3],PT(R11)-PT(AR_BSPSTORE) // load ar.bspstore (may be garbage)
ld8 r18=[r2],PT(R9)-PT(B6) // load b6
@ -754,7 +754,14 @@ ENTRY(ia64_leave_syscall)
(pUStk) ld4 r17=[r3] // r17 = cpu_data->phys_stacked_size_p8
mov.m ar.csd=r0 // M2 clear ar.csd
mov f10=f0 // clear f10
nop.m 0
movl r14=__kernel_syscall_via_epc // X
;;
nop.m 0
nop.m 0
mov b7=r14 // I0 clear b7 (hint with __kernel_syscall_via_epc)
mov r14=r0 // clear r14
mov f11=f0 // clear f11
(pKStk) br.cond.dpnt.many skip_rbs_switch