Re: [Qemu-devel] [PATCH 2/2] trace: separate MMIO tracepoints from TB-access tracepoints

[Hollis Blanchard <hollis_blanchard@mentor.com>]

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Paolo, is it true that only TB-invalidating writes go through the
io_mem_notdirty path? I'm looking at the live migration code now, and
it seems like every memory write will go through that path when global
dirty memory logging is enabled.

-- 
Hollis Blanchard <hollis_blanchard@mentor.com>
Mentor Graphics Emulation DivisionOn Wed, 2016-02-17 at 13:29 -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 <hollis_blanchard@mentor.com>
> 
> ---
> 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.
> ---
>  memory.c     | 25 +++++++++++++++++++++++++
>  trace-events |  2 ++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/memory.c b/memory.c
> index 6ae7bae..3d125c9 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -403,6 +403,11 @@ 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(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_ops_tb_read(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(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(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_ops_tb_read(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(cpu_index, mr, abs_addr, tmp,
> size);
> @@ -454,6 +464,11 @@ 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(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_ops_tb_read(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(cpu_index, mr, abs_addr, tmp,
> size);
> @@ -479,6 +494,11 @@ static MemTxResult
> memory_region_oldmmio_write_accessor(MemoryRegion *mr,
>      tmp = (*value >> shift) & mask;
>      if (mr->subpage) {
>          trace_memory_region_subpage_write(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_ops_tb_write(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(cpu_index, mr, abs_addr, tmp,
> size);
> @@ -504,6 +524,11 @@ static MemTxResult
> memory_region_write_accessor(MemoryRegion *mr,
>      tmp = (*value >> shift) & mask;
>      if (mr->subpage) {
>          trace_memory_region_subpage_write(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_ops_tb_write(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(cpu_index, mr, abs_addr, tmp,
> size);
> diff --git a/trace-events b/trace-events
> index 756ce86..7994420 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -1630,6 +1630,8 @@ 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_ops_tb_read(int cpu_index, uint64_t addr, uint64_t
> value, unsigned size) "cpu %d addr %#"PRIx64" value %#"PRIx64" size
> %u"
> +memory_region_ops_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)"

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