diff options
Diffstat (limited to 'shared/fileIO.cpp')
| -rw-r--r-- | shared/fileIO.cpp | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/shared/fileIO.cpp b/shared/fileIO.cpp index c4825e04..92fb7193 100644 --- a/shared/fileIO.cpp +++ b/shared/fileIO.cpp @@ -29,6 +29,30 @@ FileInput::FileInput(const Zstring& filename) : //throw FileError() NULL, OPEN_EXISTING, FILE_FLAG_SEQUENTIAL_SCAN, + /* possible values: (Reference http://msdn.microsoft.com/en-us/library/aa363858(VS.85).aspx#caching_behavior) + FILE_FLAG_NO_BUFFERING + FILE_FLAG_RANDOM_ACCESS + FILE_FLAG_SEQUENTIAL_SCAN + + tests on Win7 x64 show that FILE_FLAG_SEQUENTIAL_SCAN provides best performance for binary comparison in all cases: + - comparing different physical disks (DVD <-> HDD and HDD <-> HDD) + - even on same physical disk! (HDD <-> HDD) + - independent from client buffer size! + + tests on XP show that FILE_FLAG_SEQUENTIAL_SCAN provides best performance for binary comparison when + - comparing different physical disks (DVD <-> HDD) + + while FILE_FLAG_RANDOM_ACCESS offers best performance for + - same physical disk (HDD <-> HDD) + + Problem: bad XP implementation of prefetch makes flag FILE_FLAG_SEQUENTIAL_SCAN effectively load two files at once from one drive + swapping every 64 kB (or similar). File access times explode! + => For XP it is critical to use FILE_FLAG_RANDOM_ACCESS (to disable prefetch) if reading two files on same disk and + FILE_FLAG_SEQUENTIAL_SCAN when reading from different disk (e.g. massive performance improvement compared to random access for DVD <-> HDD!) + => there is no compromise that satisfies all cases! (on XP) + + for FFS most comparisons are probably between different disks => let's use FILE_FLAG_SEQUENTIAL_SCAN + */ NULL); if (fileHandle == INVALID_HANDLE_VALUE) throw FileError(wxString(_("Error opening file:")) + wxT("\n\"") + zToWx(filename_) + wxT("\"") + |