* [Qemu-devel] [PATCH 0/3] target/arm: Reduce tlb_flush overhead
@ 2018-10-18 18:27 Richard Henderson
2018-10-18 18:27 ` [Qemu-devel] [PATCH 1/3] target/arm: Remove writefn from TTBR0_EL3 Richard Henderson
` (2 more replies)
0 siblings, 3 replies; 8+ messages in thread
From: Richard Henderson @ 2018-10-18 18:27 UTC (permalink / raw)
To: qemu-devel; +Cc: peter.maydell
While installing AArch64 Ubuntu into a new vm,
I happened to notice that tlb_flush+memset was
consuming 25% of the total runtime.
This patch set reduces that overhead to 10%.
Full tlb flushes are down to 11k from 1.8M,
when pausing the installation at the first menu.
r~
Richard Henderson (3):
target/arm: Remove writefn from TTBR0_EL3
target/arm: Only flush tlb if ASID changes
target/arm: Flush only the TLBs affected by TTBR*_EL1
target/arm/helper.c | 26 +++++++++++++-------------
1 file changed, 13 insertions(+), 13 deletions(-)
--
2.17.2
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Qemu-devel] [PATCH 1/3] target/arm: Remove writefn from TTBR0_EL3
2018-10-18 18:27 [Qemu-devel] [PATCH 0/3] target/arm: Reduce tlb_flush overhead Richard Henderson
@ 2018-10-18 18:27 ` Richard Henderson
2018-10-18 20:28 ` Aaron Lindsay
2018-10-18 18:27 ` [Qemu-devel] [PATCH 2/3] target/arm: Only flush tlb if ASID changes Richard Henderson
2018-10-18 18:27 ` [Qemu-devel] [PATCH 3/3] target/arm: Flush only the TLBs affected by TTBR*_EL1 Richard Henderson
2 siblings, 1 reply; 8+ messages in thread
From: Richard Henderson @ 2018-10-18 18:27 UTC (permalink / raw)
To: qemu-devel; +Cc: peter.maydell
The EL3 version of this register does not include an ASID,
and so the tlb_flush performed by vmsa_ttbr_write is not needed.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
target/arm/helper.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/target/arm/helper.c b/target/arm/helper.c
index e3946562aa..24bbde4f76 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -4214,7 +4214,7 @@ static const ARMCPRegInfo el3_cp_reginfo[] = {
.fieldoffset = offsetof(CPUARMState, cp15.mvbar) },
{ .name = "TTBR0_EL3", .state = ARM_CP_STATE_AA64,
.opc0 = 3, .opc1 = 6, .crn = 2, .crm = 0, .opc2 = 0,
- .access = PL3_RW, .writefn = vmsa_ttbr_write, .resetvalue = 0,
+ .access = PL3_RW, .resetvalue = 0,
.fieldoffset = offsetof(CPUARMState, cp15.ttbr0_el[3]) },
{ .name = "TCR_EL3", .state = ARM_CP_STATE_AA64,
.opc0 = 3, .opc1 = 6, .crn = 2, .crm = 0, .opc2 = 2,
--
2.17.2
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [Qemu-devel] [PATCH 2/3] target/arm: Only flush tlb if ASID changes
2018-10-18 18:27 [Qemu-devel] [PATCH 0/3] target/arm: Reduce tlb_flush overhead Richard Henderson
2018-10-18 18:27 ` [Qemu-devel] [PATCH 1/3] target/arm: Remove writefn from TTBR0_EL3 Richard Henderson
@ 2018-10-18 18:27 ` Richard Henderson
2018-10-18 20:28 ` Aaron Lindsay
2018-10-18 18:27 ` [Qemu-devel] [PATCH 3/3] target/arm: Flush only the TLBs affected by TTBR*_EL1 Richard Henderson
2 siblings, 1 reply; 8+ messages in thread
From: Richard Henderson @ 2018-10-18 18:27 UTC (permalink / raw)
To: qemu-devel; +Cc: peter.maydell
Since QEMU does not implement ASIDs, changes to the ASID must flush the
tlb. However, if the ASID does not change there is no reason to flush.
In testing a boot of the Ubuntu installer to the first menu, this reduces
the number of flushes by 30%, or nearly 600k instances.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
target/arm/helper.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/target/arm/helper.c b/target/arm/helper.c
index 24bbde4f76..ed70ac645e 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -2709,12 +2709,10 @@ static void vmsa_tcr_el1_write(CPUARMState *env, const ARMCPRegInfo *ri,
static void vmsa_ttbr_write(CPUARMState *env, const ARMCPRegInfo *ri,
uint64_t value)
{
- /* 64 bit accesses to the TTBRs can change the ASID and so we
- * must flush the TLB.
- */
- if (cpreg_field_is_64bit(ri)) {
+ /* If the ASID changes (with a 64-bit write), we must flush the TLB. */
+ if (cpreg_field_is_64bit(ri) &&
+ extract64(raw_read(env, ri) ^ value, 48, 16) != 0) {
ARMCPU *cpu = arm_env_get_cpu(env);
-
tlb_flush(CPU(cpu));
}
raw_write(env, ri, value);
--
2.17.2
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [Qemu-devel] [PATCH 3/3] target/arm: Flush only the TLBs affected by TTBR*_EL1
2018-10-18 18:27 [Qemu-devel] [PATCH 0/3] target/arm: Reduce tlb_flush overhead Richard Henderson
2018-10-18 18:27 ` [Qemu-devel] [PATCH 1/3] target/arm: Remove writefn from TTBR0_EL3 Richard Henderson
2018-10-18 18:27 ` [Qemu-devel] [PATCH 2/3] target/arm: Only flush tlb if ASID changes Richard Henderson
@ 2018-10-18 18:27 ` Richard Henderson
2018-10-18 20:27 ` Aaron Lindsay
2 siblings, 1 reply; 8+ messages in thread
From: Richard Henderson @ 2018-10-18 18:27 UTC (permalink / raw)
To: qemu-devel; +Cc: peter.maydell
Only the EL0 and EL1 TLBs are affected by the EL1 register,
so flush only 2 of the 8 TLBs.
In testing a boot of the Ubuntu installer to the first menu, this
accounts for nearly all of the full tlb flushes: all but 11k of
the 1.2M instances without the patch.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
target/arm/helper.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/target/arm/helper.c b/target/arm/helper.c
index ed70ac645e..a943e91666 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -2706,14 +2706,16 @@ static void vmsa_tcr_el1_write(CPUARMState *env, const ARMCPRegInfo *ri,
tcr->raw_tcr = value;
}
-static void vmsa_ttbr_write(CPUARMState *env, const ARMCPRegInfo *ri,
- uint64_t value)
+static void vmsa_ttbr1_write(CPUARMState *env, const ARMCPRegInfo *ri,
+ uint64_t value)
{
/* If the ASID changes (with a 64-bit write), we must flush the TLB. */
if (cpreg_field_is_64bit(ri) &&
extract64(raw_read(env, ri) ^ value, 48, 16) != 0) {
ARMCPU *cpu = arm_env_get_cpu(env);
- tlb_flush(CPU(cpu));
+ tlb_flush_by_mmuidx(CPU(cpu),
+ ARMMMUIdxBit_S12NSE1 |
+ ARMMMUIdxBit_S12NSE0);
}
raw_write(env, ri, value);
}
@@ -2761,12 +2763,12 @@ static const ARMCPRegInfo vmsa_cp_reginfo[] = {
.fieldoffset = offsetof(CPUARMState, cp15.esr_el[1]), .resetvalue = 0, },
{ .name = "TTBR0_EL1", .state = ARM_CP_STATE_BOTH,
.opc0 = 3, .opc1 = 0, .crn = 2, .crm = 0, .opc2 = 0,
- .access = PL1_RW, .writefn = vmsa_ttbr_write, .resetvalue = 0,
+ .access = PL1_RW, .writefn = vmsa_ttbr1_write, .resetvalue = 0,
.bank_fieldoffsets = { offsetof(CPUARMState, cp15.ttbr0_s),
offsetof(CPUARMState, cp15.ttbr0_ns) } },
{ .name = "TTBR1_EL1", .state = ARM_CP_STATE_BOTH,
.opc0 = 3, .opc1 = 0, .crn = 2, .crm = 0, .opc2 = 1,
- .access = PL1_RW, .writefn = vmsa_ttbr_write, .resetvalue = 0,
+ .access = PL1_RW, .writefn = vmsa_ttbr1_write, .resetvalue = 0,
.bank_fieldoffsets = { offsetof(CPUARMState, cp15.ttbr1_s),
offsetof(CPUARMState, cp15.ttbr1_ns) } },
{ .name = "TCR_EL1", .state = ARM_CP_STATE_AA64,
@@ -3018,12 +3020,12 @@ static const ARMCPRegInfo lpae_cp_reginfo[] = {
.access = PL1_RW, .type = ARM_CP_64BIT | ARM_CP_ALIAS,
.bank_fieldoffsets = { offsetof(CPUARMState, cp15.ttbr0_s),
offsetof(CPUARMState, cp15.ttbr0_ns) },
- .writefn = vmsa_ttbr_write, },
+ .writefn = vmsa_ttbr1_write, },
{ .name = "TTBR1", .cp = 15, .crm = 2, .opc1 = 1,
.access = PL1_RW, .type = ARM_CP_64BIT | ARM_CP_ALIAS,
.bank_fieldoffsets = { offsetof(CPUARMState, cp15.ttbr1_s),
offsetof(CPUARMState, cp15.ttbr1_ns) },
- .writefn = vmsa_ttbr_write, },
+ .writefn = vmsa_ttbr1_write, },
REGINFO_SENTINEL
};
--
2.17.2
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [Qemu-devel] [PATCH 3/3] target/arm: Flush only the TLBs affected by TTBR*_EL1
2018-10-18 18:27 ` [Qemu-devel] [PATCH 3/3] target/arm: Flush only the TLBs affected by TTBR*_EL1 Richard Henderson
@ 2018-10-18 20:27 ` Aaron Lindsay
2018-10-18 20:52 ` Richard Henderson
0 siblings, 1 reply; 8+ messages in thread
From: Aaron Lindsay @ 2018-10-18 20:27 UTC (permalink / raw)
To: Richard Henderson; +Cc: qemu-devel, peter.maydell
On Oct 18 11:27, Richard Henderson wrote:
> @@ -2761,12 +2763,12 @@ static const ARMCPRegInfo vmsa_cp_reginfo[] = {
> .fieldoffset = offsetof(CPUARMState, cp15.esr_el[1]), .resetvalue = 0, },
> { .name = "TTBR0_EL1", .state = ARM_CP_STATE_BOTH,
> .opc0 = 3, .opc1 = 0, .crn = 2, .crm = 0, .opc2 = 0,
> - .access = PL1_RW, .writefn = vmsa_ttbr_write, .resetvalue = 0,
> + .access = PL1_RW, .writefn = vmsa_ttbr1_write, .resetvalue = 0,
It's a little confusing that vmsa_ttbr1_write is used for TTBR0_EL1. Is
the '1' indicating the EL instead of which TTBR is being used?
-Aaron
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [Qemu-devel] [PATCH 1/3] target/arm: Remove writefn from TTBR0_EL3
2018-10-18 18:27 ` [Qemu-devel] [PATCH 1/3] target/arm: Remove writefn from TTBR0_EL3 Richard Henderson
@ 2018-10-18 20:28 ` Aaron Lindsay
0 siblings, 0 replies; 8+ messages in thread
From: Aaron Lindsay @ 2018-10-18 20:28 UTC (permalink / raw)
To: Richard Henderson; +Cc: qemu-devel, peter.maydell
On Oct 18 11:27, Richard Henderson wrote:
> The EL3 version of this register does not include an ASID,
> and so the tlb_flush performed by vmsa_ttbr_write is not needed.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Aaron Lindsay <aaron@os.amperecomputing.com>
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [Qemu-devel] [PATCH 2/3] target/arm: Only flush tlb if ASID changes
2018-10-18 18:27 ` [Qemu-devel] [PATCH 2/3] target/arm: Only flush tlb if ASID changes Richard Henderson
@ 2018-10-18 20:28 ` Aaron Lindsay
0 siblings, 0 replies; 8+ messages in thread
From: Aaron Lindsay @ 2018-10-18 20:28 UTC (permalink / raw)
To: Richard Henderson; +Cc: qemu-devel, peter.maydell
On Oct 18 11:27, Richard Henderson wrote:
> Since QEMU does not implement ASIDs, changes to the ASID must flush the
> tlb. However, if the ASID does not change there is no reason to flush.
>
> In testing a boot of the Ubuntu installer to the first menu, this reduces
> the number of flushes by 30%, or nearly 600k instances.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Aaron Lindsay <aaron@os.amperecomputing.com>
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [Qemu-devel] [PATCH 3/3] target/arm: Flush only the TLBs affected by TTBR*_EL1
2018-10-18 20:27 ` Aaron Lindsay
@ 2018-10-18 20:52 ` Richard Henderson
0 siblings, 0 replies; 8+ messages in thread
From: Richard Henderson @ 2018-10-18 20:52 UTC (permalink / raw)
To: Aaron Lindsay; +Cc: qemu-devel, peter.maydell
On 10/18/18 1:27 PM, Aaron Lindsay wrote:
> On Oct 18 11:27, Richard Henderson wrote:
>> @@ -2761,12 +2763,12 @@ static const ARMCPRegInfo vmsa_cp_reginfo[] = {
>> .fieldoffset = offsetof(CPUARMState, cp15.esr_el[1]), .resetvalue = 0, },
>> { .name = "TTBR0_EL1", .state = ARM_CP_STATE_BOTH,
>> .opc0 = 3, .opc1 = 0, .crn = 2, .crm = 0, .opc2 = 0,
>> - .access = PL1_RW, .writefn = vmsa_ttbr_write, .resetvalue = 0,
>> + .access = PL1_RW, .writefn = vmsa_ttbr1_write, .resetvalue = 0,
>
> It's a little confusing that vmsa_ttbr1_write is used for TTBR0_EL1. Is
> the '1' indicating the EL instead of which TTBR is being used?
Yes. Perhaps I should have included "_el" in the symbol for clarity.
I expect to add a different function (vmsr_ttbr_el2_write?), for TTBR{0,1}_EL2,
which will also check HCR_EL2.E2H, when I get around to implementing ARMv8.1-VHE.
r~
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2018-10-18 20:52 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
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2018-10-18 18:27 [Qemu-devel] [PATCH 0/3] target/arm: Reduce tlb_flush overhead Richard Henderson
2018-10-18 18:27 ` [Qemu-devel] [PATCH 1/3] target/arm: Remove writefn from TTBR0_EL3 Richard Henderson
2018-10-18 20:28 ` Aaron Lindsay
2018-10-18 18:27 ` [Qemu-devel] [PATCH 2/3] target/arm: Only flush tlb if ASID changes Richard Henderson
2018-10-18 20:28 ` Aaron Lindsay
2018-10-18 18:27 ` [Qemu-devel] [PATCH 3/3] target/arm: Flush only the TLBs affected by TTBR*_EL1 Richard Henderson
2018-10-18 20:27 ` Aaron Lindsay
2018-10-18 20:52 ` Richard Henderson
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