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os/bluestore: avoid unneeded BlobRefing in _do_read().

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The hottest place in the terms of CPU cycles according to `perf annotate`:
```
       |          intrusive_ptr(intrusive_ptr const & rhs): px( rhs.px )
  0,04 | 365:   mov    0x28(%rax),%r12
       |          {
       |              if( px != 0 ) intrusive_ptr_add_ref( px );
  0,41 |        test   %r12,%r12
       |      ↓ je     37c
       |      _ZNSt13__atomic_baseIiEppEv():
  0,04 |        lock   addl   $0x1,(%r12)
 19,75 |        mov    0xa8(%rsp),%rax
       |      _ZN9BlueStore8_do_readEPNS_10CollectionEN5boost13intrusive_ptrINS_5OnodeEEEmmRN4ceph6buffer4listEj():
       |          }
       |          BlobRef bptr = lp->blob;
       |          unsigned l_off = pos - lp->logical_offset
       | 37c:   mov    0xa0(%rsp),%rdx
       |        sub    0x18(%rax),%edx
       |          unsigned b_off = l_off + lp->blob_offset;
  0,08 |        mov    0x1c(%rax),%ecx
```

With the patch applied:

```
       |          T * operator->() const
       |          {
       |              BOOST_ASSERT( px != 0 );
       |              return px;
       |        mov    0x28(%rcx),%rax
       |        mov    0x8(%rax),%rax
       |      _ZN9BlueStore8_do_readEPNS_10CollectionEN5boost13intrusive_ptrINS
       |          unsigned b_len = std::min(left, lp->length - l_off);
       |
       |          ready_regions_t cache_res;
       |          interval_set<uint32_t> cache_interval;
       |          bptr->shared_blob->bc.read(
 17,78 |        lea    0x18(%rax),%rdi
       |      _ZNK5boost13intrusive_ptrIN9BlueStore10CollectionEEcvbEv():
       |      #if !defined( BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS ) && !
       |          && !(defined(__SUNPRO_CC) && BOOST_WORKAROUND(__SUNPRO_CC, <=
       |
       |          explicit operator bool () const BOOST_NOEXCEPT
       |          {
       |              return px != 0;
  0,07 |        mov    0x8(%rax),%rax
```

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>
This commit is contained in:
Radoslaw Zarzynski 2018-01-05 03:30:22 +01:00
parent 43b88419d4
commit 3e2bbdfab1
1 changed files with 3 additions and 3 deletions
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6
src/os/bluestore/BlueStore.cc
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@ -6613,7 +6613,7 @@ int BlueStore::_do_read(
pos += hole;
left -= hole;
}
BlobRef bptr = lp->blob;
BlobRef& bptr = lp->blob;
unsigned l_off = pos - lp->logical_offset;
unsigned b_off = l_off + lp->blob_offset;
unsigned b_len = std::min(left, lp->length - l_off);
@ -6663,7 +6663,7 @@ int BlueStore::_do_read(
vector<bufferlist> compressed_blob_bls;
IOContext ioc(cct, NULL, true); // allow EIO
for (auto& p : blobs2read) {
BlobRef bptr = p.first;
const BlobRef& bptr = p.first;
dout(20) << __func__ << " blob " << *bptr << std::hex
<< " need " << p.second << std::dec << dendl;
if (bptr->get_blob().is_compressed()) {
@ -6762,7 +6762,7 @@ int BlueStore::_do_read(
auto p = compressed_blob_bls.begin();
blobs2read_t::iterator b2r_it = blobs2read.begin();
while (b2r_it != blobs2read.end()) {
BlobRef bptr = b2r_it->first;
const BlobRef& bptr = b2r_it->first;
dout(20) << __func__ << " blob " << *bptr << std::hex
<< " need 0x" << b2r_it->second << std::dec << dendl;
if (bptr->get_blob().is_compressed()) {