Although the parameter 'cmd' is always passed by a local array variable,
and only this function modifies it, the compiler does not know this. Every
time the 'cmd' variable is updated, a memory write operation is generated.
This generates many useless instruction operations.
To guide the compiler for proper optimization, 'cmd' is defined as a local
array variable, and copied to the output parameter at a time when the
function is returned.
The optimization effect can be viewed by running the "size arm-smmu-v3.o"
command.
Before:
text data bss dec hex
28246 1332 56 29634 73c2
After:
text data bss dec hex
28134 1332 56 29522 7352
For example:
cmd[0] = FIELD_PREP(CMDQ_0_OP, ent->opcode);
case CMDQ_OP_TLBI_EL2_VA:
cmd[0] |= FIELD_PREP(CMDQ_TLBI_0_NUM, ent->tlbi.num);
cmd[0] |= FIELD_PREP(CMDQ_TLBI_0_SCALE, ent->tlbi.scale);
cmd[0] |= FIELD_PREP(CMDQ_TLBI_0_ASID, ent->tlbi.asid);
cmd[1] |= FIELD_PREP(CMDQ_TLBI_1_LEAF, ent->tlbi.leaf);
cmd[1] |= FIELD_PREP(CMDQ_TLBI_1_TTL, ent->tlbi.ttl);
cmd[1] |= FIELD_PREP(CMDQ_TLBI_1_TG, ent->tlbi.tg);
cmd[1] |= ent->tlbi.addr & CMDQ_TLBI_1_VA_MASK;
Before:
Each "cmd[0] |=" or "cmd[1] |=" operation generates a "str" instruction,
sum = 8.
ldrb w4, [x1, #8] //w4 = ent->tlbi.num
ubfiz x4, x4, #12, #5
mov w0, #0x0
orr x4, x4, x3
str x4, [x2]
autiasp
ldrb w3, [x1, #9] //w3 = ent->tlbi.scale
ubfiz x3, x3, #20, #5
orr x3, x3, x4
str x3, [x2]
ldrh w4, [x1, #10] //w4 = ent->tlbi.asid
orr x3, x3, x4, lsl #48
str x3, [x2]
ldrb w3, [x1, #14] //w3 = ent->tlbi.leaf
str x3, [x2, #8]
ldrb w4, [x1, #15] //w4 = ent->tlbi.ttl
ubfiz x4, x4, #8, #2
orr x4, x4, x3
str x4, [x2, #8]
ldrb w3, [x1, #16] //ent->tlbi.tg
ubfiz x3, x3, #10, #2
orr x3, x3, x4
str x3, [x2, #8]
ldr x1, [x1, #24] //ent->tlbi.addr
and x1, x1, #0xfffffffffffff000
orr x1, x1, x3
str x1, [x2, #8]
ret
After:
All "cmd[0] |=" and "cmd[1] |=" operations generate a "stp" instruction,
sum = 1.
3e8:
mov w0, #0x0
autiasp
stp x2, x1, [x3]
ret
bti j
3fc:
ldrb w5, [x1, #8] //w5 = ent->tlbi.num
mov x2, #0x22 //x2 = ent->opcode = CMDQ_0_OP
ldrb w6, [x1, #9] //w6 = ent->tlbi.scale
ubfiz x5, x5, #12, #5
ldrb w0, [x1, #16] //w0 = ent->tlbi.tg
orr x5, x5, x2
ldrb w7, [x1, #15] //w7 = ent->tlbi.ttl
ldr x4, [x1, #24] //x4 = ent->tlbi.addr
ubfiz x0, x0, #10, #2
ldrh w2, [x1, #10] //w2 = ent->tlbi.asid
ubfiz x6, x6, #20, #5
ldrb w8, [x1, #14] //w8 = ent->tlbi.leaf
and x4, x4, #0xfffffffffffff000
ubfiz x1, x7, #8, #2
orr x1, x0, x1
orr x2, x6, x2, lsl #48
orr x0, x4, x8
orr x2, x2, x5
orr x1, x1, x0
b 3e8
Signed-off-by: Zhen Lei <thunder.leiz...@huawei.com>
---
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index f5848b351b19359..e55dfc14cac6005 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -234,10 +234,12 @@ static int queue_remove_raw(struct arm_smmu_queue *q, u64
*ent)
}
/* High-level queue accessors */
-static int arm_smmu_cmdq_build_cmd(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
+static int arm_smmu_cmdq_build_cmd(u64 *out_cmd, struct arm_smmu_cmdq_ent *ent)
{
- memset(cmd, 0, 1 << CMDQ_ENT_SZ_SHIFT);
- cmd[0] |= FIELD_PREP(CMDQ_0_OP, ent->opcode);
+ int i;
+ u64 cmd[CMDQ_ENT_DWORDS] = {0};
+
+ cmd[0] = FIELD_PREP(CMDQ_0_OP, ent->opcode);
switch (ent->opcode) {
case CMDQ_OP_TLBI_EL2_ALL:
@@ -332,6 +334,9 @@ static int arm_smmu_cmdq_build_cmd(u64 *cmd, struct
arm_smmu_cmdq_ent *ent)
return -ENOENT;
}
+ for (i = 0; i < CMDQ_ENT_DWORDS; i++)
+ out_cmd[i] = cmd[i];
+
return 0;
}
--
2.25.1
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