Messages in this thread Patch in this message | | | From | Zhen Lei <> | Subject | [PATCH v3 1/1] iommu/arm-smmu-v3: Simplify useless instructions in arm_smmu_cmdq_build_cmd() | Date | Tue, 7 Dec 2021 17:41:09 +0800 |
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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.leizhen@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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