[Qemu-devel] [PATCH 5/9] memory: let address_space_rw/ld*/st* run outside the BQL

[Paolo Bonzini <pbonzini@redhat.com>]

From: Jan Kiszka <jan.kiszka@siemens.com>

The MMIO case is further broken up in two cases: if the caller does not
hold the BQL on invocation, the unlocked one takes or avoids BQL depending
on the locking strategy of the target memory region and its coalesced
MMIO handling.  In this case, the caller should not hold _any_ lock
(a friendly suggestion which is disregarded by virtio-scsi-dataplane).

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 exec.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 57 insertions(+), 9 deletions(-)

diff --git a/exec.c b/exec.c
index 094f87e..78c99f6 100644
--- a/exec.c
+++ b/exec.c
@@ -48,6 +48,7 @@
 #endif
 #include "exec/cpu-all.h"
 #include "qemu/rcu_queue.h"
+#include "qemu/main-loop.h"
 #include "exec/cputlb.h"
 #include "translate-all.h"
 
@@ -2318,11 +2319,27 @@ static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr)
     return l;
 }
 
-static void prepare_mmio_access(MemoryRegion *mr)
+static bool prepare_mmio_access(MemoryRegion *mr)
 {
+    bool unlocked = !qemu_mutex_iothread_locked();
+    bool release_lock = false;
+
+    if (unlocked && mr->global_locking) {
+        qemu_mutex_lock_iothread();
+        unlocked = false;
+        release_lock = true;
+    }
     if (mr->flush_coalesced_mmio) {
+        if (unlocked) {
+            qemu_mutex_lock_iothread();
+        }
         qemu_flush_coalesced_mmio_buffer();
+        if (unlocked) {
+            qemu_mutex_unlock_iothread();
+        }
     }
+
+    return release_lock;
 }
 
 MemTxResult address_space_rw(AddressSpace *as, hwaddr addr, MemTxAttrs attrs,
@@ -2334,6 +2351,7 @@ MemTxResult address_space_rw(AddressSpace *as, hwaddr addr, MemTxAttrs attrs,
     hwaddr addr1;
     MemoryRegion *mr;
     MemTxResult result = MEMTX_OK;
+    bool release_lock = false;
 
     rcu_read_lock();
     while (len > 0) {
@@ -2342,7 +2360,7 @@ MemTxResult address_space_rw(AddressSpace *as, hwaddr addr, MemTxAttrs attrs,
 
         if (is_write) {
             if (!memory_access_is_direct(mr, is_write)) {
-                prepare_mmio_access(mr);
+                release_lock |= prepare_mmio_access(mr);
                 l = memory_access_size(mr, l, addr1);
                 /* XXX: could force current_cpu to NULL to avoid
                    potential bugs */
@@ -2384,7 +2402,7 @@ MemTxResult address_space_rw(AddressSpace *as, hwaddr addr, MemTxAttrs attrs,
         } else {
             if (!memory_access_is_direct(mr, is_write)) {
                 /* I/O case */
-                prepare_mmio_access(mr);
+                release_lock |= prepare_mmio_access(mr);
                 l = memory_access_size(mr, l, addr1);
                 switch (l) {
                 case 8:
@@ -2420,6 +2438,12 @@ MemTxResult address_space_rw(AddressSpace *as, hwaddr addr, MemTxAttrs attrs,
                 memcpy(buf, ptr, l);
             }
         }
+
+        if (release_lock) {
+            qemu_mutex_unlock_iothread();
+            release_lock = false;
+        }
+
         len -= l;
         buf += l;
         addr += l;
@@ -2746,11 +2770,12 @@ static inline uint32_t address_space_ldl_internal(AddressSpace *as, hwaddr addr,
     hwaddr l = 4;
     hwaddr addr1;
     MemTxResult r;
+    bool release_lock = false;
 
     rcu_read_lock();
     mr = address_space_translate(as, addr, &addr1, &l, false);
     if (l < 4 || !memory_access_is_direct(mr, false)) {
-        prepare_mmio_access(mr);
+        release_lock |= prepare_mmio_access(mr);
 
         /* I/O case */
         r = memory_region_dispatch_read(mr, addr1, &val, 4, attrs);
@@ -2784,6 +2809,9 @@ static inline uint32_t address_space_ldl_internal(AddressSpace *as, hwaddr addr,
     if (result) {
         *result = r;
     }
+    if (release_lock) {
+        qemu_mutex_unlock_iothread();
+    }
     rcu_read_unlock();
     return val;
 }
@@ -2836,12 +2864,13 @@ static inline uint64_t address_space_ldq_internal(AddressSpace *as, hwaddr addr,
     hwaddr l = 8;
     hwaddr addr1;
     MemTxResult r;
+    bool release_lock = false;
 
     rcu_read_lock();
     mr = address_space_translate(as, addr, &addr1, &l,
                                  false);
     if (l < 8 || !memory_access_is_direct(mr, false)) {
-        prepare_mmio_access(mr);
+        release_lock |= prepare_mmio_access(mr);
 
         /* I/O case */
         r = memory_region_dispatch_read(mr, addr1, &val, 8, attrs);
@@ -2875,6 +2904,9 @@ static inline uint64_t address_space_ldq_internal(AddressSpace *as, hwaddr addr,
     if (result) {
         *result = r;
     }
+    if (release_lock) {
+        qemu_mutex_unlock_iothread();
+    }
     rcu_read_unlock();
     return val;
 }
@@ -2947,12 +2979,13 @@ static inline uint32_t address_space_lduw_internal(AddressSpace *as,
     hwaddr l = 2;
     hwaddr addr1;
     MemTxResult r;
+    bool release_lock = false;
 
     rcu_read_lock();
     mr = address_space_translate(as, addr, &addr1, &l,
                                  false);
     if (l < 2 || !memory_access_is_direct(mr, false)) {
-        prepare_mmio_access(mr);
+        release_lock |= prepare_mmio_access(mr);
 
         /* I/O case */
         r = memory_region_dispatch_read(mr, addr1, &val, 2, attrs);
@@ -2986,6 +3019,9 @@ static inline uint32_t address_space_lduw_internal(AddressSpace *as,
     if (result) {
         *result = r;
     }
+    if (release_lock) {
+        qemu_mutex_unlock_iothread();
+    }
     rcu_read_unlock();
     return val;
 }
@@ -3037,12 +3073,13 @@ void address_space_stl_notdirty(AddressSpace *as, hwaddr addr, uint32_t val,
     hwaddr l = 4;
     hwaddr addr1;
     MemTxResult r;
+    bool release_lock = false;
 
     rcu_read_lock();
     mr = address_space_translate(as, addr, &addr1, &l,
                                  true);
     if (l < 4 || !memory_access_is_direct(mr, true)) {
-        prepare_mmio_access(mr);
+        release_lock |= prepare_mmio_access(mr);
 
         r = memory_region_dispatch_write(mr, addr1, val, 4, attrs);
     } else {
@@ -3063,6 +3100,9 @@ void address_space_stl_notdirty(AddressSpace *as, hwaddr addr, uint32_t val,
     if (result) {
         *result = r;
     }
+    if (release_lock) {
+        qemu_mutex_unlock_iothread();
+    }
     rcu_read_unlock();
 }
 
@@ -3083,12 +3123,13 @@ static inline void address_space_stl_internal(AddressSpace *as,
     hwaddr l = 4;
     hwaddr addr1;
     MemTxResult r;
+    bool release_lock = false;
 
     rcu_read_lock();
     mr = address_space_translate(as, addr, &addr1, &l,
                                  true);
     if (l < 4 || !memory_access_is_direct(mr, true)) {
-        prepare_mmio_access(mr);
+        release_lock |= prepare_mmio_access(mr);
 
 #if defined(TARGET_WORDS_BIGENDIAN)
         if (endian == DEVICE_LITTLE_ENDIAN) {
@@ -3121,6 +3162,9 @@ static inline void address_space_stl_internal(AddressSpace *as,
     if (result) {
         *result = r;
     }
+    if (release_lock) {
+        qemu_mutex_unlock_iothread();
+    }
     rcu_read_unlock();
 }
 
@@ -3190,11 +3234,12 @@ static inline void address_space_stw_internal(AddressSpace *as,
     hwaddr l = 2;
     hwaddr addr1;
     MemTxResult r;
+    bool release_lock = false;
 
     rcu_read_lock();
     mr = address_space_translate(as, addr, &addr1, &l, true);
     if (l < 2 || !memory_access_is_direct(mr, true)) {
-        prepare_mmio_access(mr);
+        release_lock |= prepare_mmio_access(mr);
 
 #if defined(TARGET_WORDS_BIGENDIAN)
         if (endian == DEVICE_LITTLE_ENDIAN) {
@@ -3227,6 +3272,9 @@ static inline void address_space_stw_internal(AddressSpace *as,
     if (result) {
         *result = r;
     }
+    if (release_lock) {
+        qemu_mutex_unlock_iothread();
+    }
     rcu_read_unlock();
 }
 
-- 
1.8.3.1