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sparc64: speed up etrap/rtrap on NG2 and later processors

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For many sun4v processor types, reading or writing a privileged register
has a latency of 40 to 70 cycles.  Use a combination of the low-latency
allclean, otherw, normalw, and nop instructions in etrap and rtrap to
replace 2 rdpr and 5 wrpr instructions and improve etrap/rtrap
performance.  allclean, otherw, and normalw are available on NG2 and
later processors.

The average ticks to execute the flush windows trap ("ta 0x3") with and
without this patch on select platforms:

 CPU            Not patched     Patched    % Latency Reduction

 NG2            1762            1558            -11.58
 NG4            3619            3204            -11.47
 M7             3015            2624            -12.97
 SPARC64-X      829             770              -7.12

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Anthony Yznaga
2017-08-18 12:40:36 -07:00
committed by David S. Miller
parent 5bd0ea9107
commit a7159a87a3
5 changed files with 45 additions and 6 deletions
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13
arch/sparc/kernel/rtrap_64.S
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@@ -224,10 +224,19 @@ rt_continue: ldx [%sp + PTREGS_OFF + PT_V9_G1], %g1
rdpr %otherwin, %l2
srl %l1, 3, %l1
wrpr %l2, %g0, %canrestore
661: wrpr %l2, %g0, %canrestore
.section .fast_win_ctrl_1insn_patch, "ax"
.word 661b
.word 0x89880000 ! normalw
.previous
wrpr %l1, %g0, %wstate
brnz,pt %l2, user_rtt_restore
wrpr %g0, %g0, %otherwin
661: wrpr %g0, %g0, %otherwin
.section .fast_win_ctrl_1insn_patch, "ax"
.word 661b
nop
.previous
ldx [%g6 + TI_FLAGS], %g3
wr %g0, ASI_AIUP, %asi