diff mbox series

[v3,1/2] target/riscv: Emulate TIME CSRs for privileged mode

Message ID 20200202134217.14264-2-anup.patel@wdc.com (mailing list archive)
State New, archived
Headers show
Series RISC-V TIME CSR for privileged mode | expand

Commit Message

Anup Patel Feb. 2, 2020, 1:42 p.m. UTC 
Currently, TIME CSRs are emulated only for user-only mode. This
patch add TIME CSRs emulation for privileged mode.

For privileged mode, the TIME CSRs will return value provided
by rdtime callback which is registered by QEMU machine/platform
emulation (i.e. CLINT emulation). If rdtime callback is not
available then the monitor (i.e. OpenSBI) will trap-n-emulate
TIME CSRs in software.

We see 25+% performance improvement in hackbench numbers when
TIME CSRs are not trap-n-emulated.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
---
 target/riscv/cpu.h        |  5 +++
 target/riscv/cpu_helper.c |  5 +++
 target/riscv/csr.c        | 86 +++++++++++++++++++++++++++++++++++++--
 3 files changed, 92 insertions(+), 4 deletions(-)

Comments

Bin Meng March 1, 2020, 8:22 a.m. UTC | #1 
On Sun, Feb 2, 2020 at 9:44 PM Anup Patel <anup.patel@wdc.com> wrote:
>
> Currently, TIME CSRs are emulated only for user-only mode. This
> patch add TIME CSRs emulation for privileged mode.
>
> For privileged mode, the TIME CSRs will return value provided
> by rdtime callback which is registered by QEMU machine/platform
> emulation (i.e. CLINT emulation). If rdtime callback is not
> available then the monitor (i.e. OpenSBI) will trap-n-emulate
> TIME CSRs in software.
>
> We see 25+% performance improvement in hackbench numbers when
> TIME CSRs are not trap-n-emulated.
>
> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
> ---
>  target/riscv/cpu.h        |  5 +++
>  target/riscv/cpu_helper.c |  5 +++
>  target/riscv/csr.c        | 86 +++++++++++++++++++++++++++++++++++++--
>  3 files changed, 92 insertions(+), 4 deletions(-)
>

Jonathan has a patch before:
http://patchwork.ozlabs.org/patch/1106480/

The idea in his patch does similar thing according to mcounteren.TM.
But in this patch we seem to control the TIME CSR purely by software.
Is this behavior spec complaint?

Regards,
Bin
diff mbox series

Patch

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index d52f209361..3dcdf92227 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -159,6 +159,7 @@  struct CPURISCVState {
     target_ulong htval;
     target_ulong htinst;
     target_ulong hgatp;
+    uint64_t htimedelta;
 
     /* Virtual CSRs */
     target_ulong vsstatus;
@@ -201,6 +202,9 @@  struct CPURISCVState {
     /* physical memory protection */
     pmp_table_t pmp_state;
 
+    /* machine specific rdtime callback */
+    uint64_t (*rdtime_fn)(void);
+
     /* True if in debugger mode.  */
     bool debugger;
 #endif
@@ -322,6 +326,7 @@  void riscv_cpu_swap_hypervisor_regs(CPURISCVState *env);
 int riscv_cpu_claim_interrupts(RISCVCPU *cpu, uint32_t interrupts);
 uint32_t riscv_cpu_update_mip(RISCVCPU *cpu, uint32_t mask, uint32_t value);
 #define BOOL_TO_MASK(x) (-!!(x)) /* helper for riscv_cpu_update_mip value */
+void riscv_cpu_set_rdtime_fn(CPURISCVState *env, uint64_t (*fn)(void));
 #endif
 void riscv_cpu_set_mode(CPURISCVState *env, target_ulong newpriv);
 
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index b9e90dfd9a..cc9f20b471 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -258,6 +258,11 @@  uint32_t riscv_cpu_update_mip(RISCVCPU *cpu, uint32_t mask, uint32_t value)
     return old;
 }
 
+void riscv_cpu_set_rdtime_fn(CPURISCVState *env, uint64_t (*fn)(void))
+{
+    env->rdtime_fn = fn;
+}
+
 void riscv_cpu_set_mode(CPURISCVState *env, target_ulong newpriv)
 {
     if (newpriv > PRV_M) {
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 572a478e8c..11d184cd16 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -238,6 +238,32 @@  static int read_timeh(CPURISCVState *env, int csrno, target_ulong *val)
 
 #else /* CONFIG_USER_ONLY */
 
+static int read_time(CPURISCVState *env, int csrno, target_ulong *val)
+{
+    uint64_t delta = riscv_cpu_virt_enabled(env) ? env->htimedelta : 0;
+
+    if (!env->rdtime_fn) {
+        return -1;
+    }
+
+    *val = env->rdtime_fn() + delta;
+    return 0;
+}
+
+#if defined(TARGET_RISCV32)
+static int read_timeh(CPURISCVState *env, int csrno, target_ulong *val)
+{
+    uint64_t delta = riscv_cpu_virt_enabled(env) ? env->htimedelta : 0;
+
+    if (!env->rdtime_fn) {
+        return -1;
+    }
+
+    *val = (env->rdtime_fn() + delta) >> 32;
+    return 0;
+}
+#endif
+
 /* Machine constants */
 
 #define M_MODE_INTERRUPTS  (MIP_MSIP | MIP_MTIP | MIP_MEIP)
@@ -930,6 +956,56 @@  static int write_hgatp(CPURISCVState *env, int csrno, target_ulong val)
     return 0;
 }
 
+static int read_htimedelta(CPURISCVState *env, int csrno, target_ulong *val)
+{
+    if (!env->rdtime_fn) {
+        return -1;
+    }
+
+#if defined(TARGET_RISCV32)
+    *val = env->htimedelta & 0xffffffff;
+#else
+    *val = env->htimedelta;
+#endif
+    return 0;
+}
+
+static int write_htimedelta(CPURISCVState *env, int csrno, target_ulong val)
+{
+    if (!env->rdtime_fn) {
+        return -1;
+    }
+
+#if defined(TARGET_RISCV32)
+    env->htimedelta = deposit64(env->htimedelta, 0, 32, (uint64_t)val);
+#else
+    env->htimedelta = val;
+#endif
+    return 0;
+}
+
+#if defined(TARGET_RISCV32)
+static int read_htimedeltah(CPURISCVState *env, int csrno, target_ulong *val)
+{
+    if (!env->rdtime_fn) {
+        return -1;
+    }
+
+    *val = env->htimedelta >> 32;
+    return 0;
+}
+
+static int write_htimedeltah(CPURISCVState *env, int csrno, target_ulong val)
+{
+    if (!env->rdtime_fn) {
+        return -1;
+    }
+
+    env->htimedelta = deposit64(env->htimedelta, 32, 32, (uint64_t)val);
+    return 0;
+}
+#endif
+
 /* Virtual CSR Registers */
 static int read_vsstatus(CPURISCVState *env, int csrno, target_ulong *val)
 {
@@ -1202,14 +1278,12 @@  static riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
     [CSR_INSTRETH] =            { ctr,  read_instreth                       },
 #endif
 
-    /* User-level time CSRs are only available in linux-user
-     * In privileged mode, the monitor emulates these CSRs */
-#if defined(CONFIG_USER_ONLY)
+    /* In privileged mode, the monitor will have to emulate TIME CSRs only if
+     * rdtime callback is not provided by machine/platform emulation */
     [CSR_TIME] =                { ctr,  read_time                           },
 #if defined(TARGET_RISCV32)
     [CSR_TIMEH] =               { ctr,  read_timeh                          },
 #endif
-#endif
 
 #if !defined(CONFIG_USER_ONLY)
     /* Machine Timers and Counters */
@@ -1275,6 +1349,10 @@  static riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
     [CSR_HTVAL] =               { hmode,   read_htval,       write_htval      },
     [CSR_HTINST] =              { hmode,   read_htinst,      write_htinst     },
     [CSR_HGATP] =               { hmode,   read_hgatp,       write_hgatp      },
+    [CSR_HTIMEDELTA] =          { hmode,   read_htimedelta,  write_htimedelta },
+#if defined(TARGET_RISCV32)
+    [CSR_HTIMEDELTAH] =         { hmode,   read_htimedeltah, write_htimedeltah},
+#endif
 
     [CSR_VSSTATUS] =            { hmode,   read_vsstatus,    write_vsstatus   },
     [CSR_VSIP] =                { hmode,   NULL,     NULL,     rmw_vsip       },