Avoid mixing std::ptr::read/write_volatile() and std::ptr::copy() #111
Comments
jiangliu
added a commit
to jiangliu/vm-memory
that referenced
this issue
Aug 25, 2020
Replace std::ptr::copy() with copy_slice(). With this change applied,
most accesses to guest memory are wrapped by copy_slice() to avoid
mixing read/write_volatile() and memcpy(). The file related interfaces,
read_from()/read_exact_from()/write_to()/write_all_to(), may still
use normal memory operations.
The change causes more than 50% performance drop of
copy_to_volatile_slice() when copying 10K data buffer. The performance
drop is caused by non-optimal implemantation of copy_slice(), which
should be tracked as a dedicate issue.
Benchmarking VolatileSlice::copy_to_volatile_slice:
Collecting 200 samples in estimated 10.000 s
VolatileSlice::copy_to_volatile_slice
time: [684.24 ns 687.08 ns 691.81 ns]
change: [+134.93% +136.04% +137.32%] (p = 0.00 < 0.05)
Performance has regressed.
Found 11 outliers among 200 measurements (5.50%)
1 (0.50%) low mild
4 (2.00%) high mild
6 (3.00%) high severe
Fixes: rust-vmm#111
Signed-off-by: Liu Jiang <[email protected]>
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
The copy_slice() wrapper is used to access guest memory for most VolatileMemory methods, but there's an exception that copy_to_volatile_slice() uses std::ptr::copy(). The copy_to_volatile_slice() method should be refined to use copy_slice() so we never mix std::ptr::read/write_volatile() and std::ptr::copy()
The text was updated successfully, but these errors were encountered: