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crucible: fs: keep ioctl buffer between runs

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perf blames the SEARCH_V2 ioctl wrapper for a lot of time spent in malloc.
Use a thread_local buffer for ioctl results, and reuse it between runs.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
(cherry picked from commit e509210428)
This commit is contained in:
Zygo Blaxell
2017-02-07 21:56:54 -05:00
parent 312254a47b
commit d6f97edf4a
1 changed files with 12 additions and 2 deletions
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14
lib/fs.cc
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@ -716,10 +716,20 @@ namespace crucible {
bool
BtrfsIoctlSearchKey::do_ioctl_nothrow(int fd)
{
vector<char> ioctl_arg = vector_copy_struct<btrfs_ioctl_search_key>(this);
// Normally we like to be paranoid and fill empty bytes with zero,
// but these buffers can be huge. 80% of a 4GHz CPU huge.
ioctl_arg.resize(sizeof(btrfs_ioctl_search_args_v2) + m_buf_size);
// Keep the ioctl buffer from one run to the next to save on malloc costs
size_t target_buf_size = sizeof(btrfs_ioctl_search_args_v2) + m_buf_size;
thread_local vector<char> ioctl_arg;
if (ioctl_arg.size() < m_buf_size) {
ioctl_arg = vector_copy_struct<btrfs_ioctl_search_key>(this);
ioctl_arg.resize(target_buf_size);
} else {
memcpy(ioctl_arg.data(), static_cast<btrfs_ioctl_search_key*>(this), sizeof(btrfs_ioctl_search_key));
}
btrfs_ioctl_search_args_v2 *ioctl_ptr = reinterpret_cast<btrfs_ioctl_search_args_v2 *>(ioctl_arg.data());
ioctl_ptr->buf_size = m_buf_size;