cpu_physical_memory_sync_dirty_bitmap: Fix alignment check
PATCH 1/1 cpu_physical_memory_sync_dirty_bitmap: Fix alignment check
From: Dr. David Alan Gilbert <[email protected]>
This code has an optimised, word aligned version, and a boring unaligned version. Recently 084140bd498909 fixed a missing offset addition from the core of both versions. However, the offset isn't necessarily aligned and thus the choice between the two versions needs fixing up to also include the offset.
Symptom:
A few stuck unsent pages during migration; not normally noticed
unless under very low bandwidth in which case the migration may get stuck never ending and never performing a 2nd sync; noticed by a hanging postcopy-test on a very heavily loaded system.
--- include/exec/ram_addr.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
include/exec/ram_addr.h +3 -2
@@ -378,15 +378,16 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb, {ram_addr_t addr;unsigned long page =BIT_WORD (start >>TARGET_PAGE_BITS ); +unsigned long word =BIT_WORD ((start + rb->offset) >>TARGET_PAGE_BITS );uint64_t num_dirty =0 ;unsigned long *dest = rb->bmap;/* start address is aligned at the start of a word? */ -if (((page *BITS_PER_LONG ) <<TARGET_PAGE_BITS ) == start) { +if (((word *BITS_PER_LONG ) <<TARGET_PAGE_BITS ) == + (start + rb->offset)) {int k;int nr =BITS_TO_LONGS (length >>TARGET_PAGE_BITS );unsigned long *const *src; -unsigned long word =BIT_WORD ((start + rb->offset) >>TARGET_PAGE_BITS );unsigned long idx = (word *BITS_PER_LONG ) /DIRTY_MEMORY_BLOCK_SIZE ;unsigned long offset =BIT_WORD ((word *BITS_PER_LONG ) %DIRTY_MEMORY_BLOCK_SIZE );
Signature · 1 line
2.13.3
Quoted 28 lines · Dr. David Alan Gilbert (git)
From: Dr. David Alan Gilbert <[email protected]>
This code has an optimised, word aligned version, and a boring unaligned version. Recently
084140bd498909fixed a missing offset addition from the core of both versions. However, the offset isn't necessarily aligned and thus the choice between the two versions needs fixing up to also include the offset.Symptom:
A few stuck unsent pages during migration; not normally noticed
unless under very low bandwidth in which case the migration may get stuck never ending and never performing a 2nd sync; noticed by a hanging postcopy-test on a very heavily loaded system.Fixes 084140bd498909Signed-off-by Dr. David Alan Gilbert <[email protected]>Reported-by Alex Benneé <[email protected]>Tested-by Alex Bennée <[email protected]>--- include/exec/ram_addr.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)include/exec/ram_addr.h +0
-0
include/exec/ram_addr.h uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb, · line 380
Quoted 3 lines
include/exec/ram_addr.h +0
-0@@ -378,15 +378,16 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock *rb, {ram_addr_t addr;unsigned long page =BIT_WORD (start >>TARGET_PAGE_BITS );
Nice catch!
"page" can now be moved to the "if", exactly where you've removed the declaration of "word".
Paolo
Quoted 16 lines
include/exec/ram_addr.h +3
-2+unsigned long word =BIT_WORD ((start + rb->offset) >>TARGET_PAGE_BITS );uint64_t num_dirty =0 ;unsigned long *dest = rb->bmap;/* start address is aligned at the start of a word? */ -if (((page *BITS_PER_LONG ) <<TARGET_PAGE_BITS ) == start) { +if (((word *BITS_PER_LONG ) <<TARGET_PAGE_BITS ) == + (start + rb->offset)) {int k;int nr =BITS_TO_LONGS (length >>TARGET_PAGE_BITS );unsigned long *const *src; -unsigned long word =BIT_WORD ((start + rb->offset) >>TARGET_PAGE_BITS );unsigned long idx = (word *BITS_PER_LONG ) /DIRTY_MEMORY_BLOCK_SIZE ;unsigned long offset =BIT_WORD ((word *BITS_PER_LONG ) %DIRTY_MEMORY_BLOCK_SIZE );