[v2,2/2] trace: separate MMIO tracepoints from TB-access tracepoints

Commit Message

Hollis Blanchard March 2, 2016, 8:12 p.m. UTC

Memory accesses to code which has previously been translated into a TB show up
in the MMIO path, so that they may invalidate the TB. It's extremely confusing
to mix those in with device MMIOs, so split them into their own tracepoint.

Signed-off-by: Hollis Blanchard <[e-mail]>
Reviewed-by: Stefan Hajnoczi <[e-mail]>
---
It took many hours to figure out why some RAM accesses were coming through the
MMIO path instead of being handled inline in the TBs.

On IRC, Paolo expressed some concern about performance, but ultimately agreed
that adding one conditional to an already heavy codepath wouldn't have much
impact.

v2: rename trace_memory_region_ops_tb_read/write to
trace_memory_region_tb_read/write
---
 memory.c     | 30 ++++++++++++++++++++++++++++++
 trace-events |  2 ++
 2 files changed, 32 insertions(+)

Comments

Hollis Blanchard March 7, 2016, 9:32 p.m. UTC | #1

On Wed, 2016-03-02 at 12:12 -0800, Hollis Blanchard wrote:
> Memory accesses to code which has previously been translated into a
> TB show up
> in the MMIO path, so that they may invalidate the TB. It's extremely
> confusing
> to mix those in with device MMIOs, so split them into their own
> tracepoint.
> 
> Signed-off-by: Hollis Blanchard <[e-mail]>
> Reviewed-by: Stefan Hajnoczi <[e-mail]>
> ---
> It took many hours to figure out why some RAM accesses were coming
> through the
> MMIO path instead of being handled inline in the TBs.
> 
> On IRC, Paolo expressed some concern about performance, but
> ultimately agreed
> that adding one conditional to an already heavy codepath wouldn't
> have much
> impact.
> 
> v2: rename trace_memory_region_ops_tb_read/write to
> trace_memory_region_tb_read/write
> 
Stefan, any further comment here? You sent a Reviewed-by on the
original, but unlike the "include CPU index" patch, you didn't mention
adding this one to https://github.com/stefanha/qemu/commits/tracing.

-- 
Hollis Blanchard <[e-mail]>
Mentor Graphics Emulation Division

Patch

diff --git a/memory.c b/memory.c
index 89395e6..84347fa 100644
--- a/memory.c
+++ b/memory.c
@@ -407,6 +407,11 @@  static MemTxResult memory_region_oldmmio_read_accessor(MemoryRegion *mr,
     tmp = mr->ops->old_mmio.read[ctz32(size)](mr->opaque, addr);
     if (mr->subpage) {
         trace_memory_region_subpage_read(get_cpu_index(), mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_tb_read(get_cpu_index(), addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_READ_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_read(get_cpu_index(), mr, abs_addr, tmp, size);
@@ -428,6 +433,11 @@  static MemTxResult  memory_region_read_accessor(MemoryRegion *mr,
     tmp = mr->ops->read(mr->opaque, addr, size);
     if (mr->subpage) {
         trace_memory_region_subpage_read(get_cpu_index(), mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_tb_read(get_cpu_index(), addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_READ_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_read(get_cpu_index(), mr, abs_addr, tmp, size);
@@ -450,6 +460,11 @@  static MemTxResult memory_region_read_with_attrs_accessor(MemoryRegion *mr,
     r = mr->ops->read_with_attrs(mr->opaque, addr, &tmp, size, attrs);
     if (mr->subpage) {
         trace_memory_region_subpage_read(get_cpu_index(), mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_tb_read(get_cpu_index(), addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_READ_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_read(get_cpu_index(), mr, abs_addr, tmp, size);
@@ -471,6 +486,11 @@  static MemTxResult memory_region_oldmmio_write_accessor(MemoryRegion *mr,
     tmp = (*value >> shift) & mask;
     if (mr->subpage) {
         trace_memory_region_subpage_write(get_cpu_index(), mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_tb_write(get_cpu_index(), addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_WRITE_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_write(get_cpu_index(), mr, abs_addr, tmp, size);
@@ -492,6 +512,11 @@  static MemTxResult memory_region_write_accessor(MemoryRegion *mr,
     tmp = (*value >> shift) & mask;
     if (mr->subpage) {
         trace_memory_region_subpage_write(get_cpu_index(), mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_tb_write(get_cpu_index(), addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_WRITE_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_write(get_cpu_index(), mr, abs_addr, tmp, size);
@@ -513,6 +538,11 @@  static MemTxResult memory_region_write_with_attrs_accessor(MemoryRegion *mr,
     tmp = (*value >> shift) & mask;
     if (mr->subpage) {
         trace_memory_region_subpage_write(get_cpu_index(), mr, addr, tmp, size);
+    } else if (mr == &io_mem_notdirty) {
+        /* Accesses to code which has previously been translated into a TB show
+         * up in the MMIO path, as accesses to the io_mem_notdirty
+         * MemoryRegion. */
+        trace_memory_region_tb_write(get_cpu_index(), addr, tmp, size);
     } else if (TRACE_MEMORY_REGION_OPS_WRITE_ENABLED) {
         hwaddr abs_addr = memory_region_to_absolute_addr(mr, addr);
         trace_memory_region_ops_write(get_cpu_index(), mr, abs_addr, tmp, size);
diff --git a/trace-events b/trace-events
index a9f33fb..5d0d483 100644
--- a/trace-events
+++ b/trace-events
@@ -1624,6 +1624,8 @@  memory_region_ops_read(int cpu_index, void *mr, uint64_t addr, uint64_t value, u
 memory_region_ops_write(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr %#"PRIx64" value %#"PRIx64" size %u"
 memory_region_subpage_read(int cpu_index, void *mr, uint64_t offset, uint64_t value, unsigned size) "cpu %d mr %p offset %#"PRIx64" value %#"PRIx64" size %u"
 memory_region_subpage_write(int cpu_index, void *mr, uint64_t offset, uint64_t value, unsigned size) "cpu %d mr %p offset %#"PRIx64" value %#"PRIx64" size %u"
+memory_region_tb_read(int cpu_index, uint64_t addr, uint64_t value, unsigned size) "cpu %d addr %#"PRIx64" value %#"PRIx64" size %u"
+memory_region_tb_write(int cpu_index, uint64_t addr, uint64_t value, unsigned size) "cpu %d addr %#"PRIx64" value %#"PRIx64" size %u"
 
 # qom/object.c
 object_dynamic_cast_assert(const char *type, const char *target, const char *file, int line, const char *func) "%s->%s (%s:%d:%s)"