QNX RTOS v4 Knowledge Base
QNX RTOS v4 Knowledge Base
| Title |
Discussion on QNX4 Fsys option -a |
| Ref. No. |
QNX.000009567 |
| Category(ies) |
Kernel, Filesystem, Configuration |
| Issue |
When we do a large number of writes to the disk, Fsys correctly caches the writes (We rebuild the OS and add the '-a' option to 'Fsys'). However, once Fsys starts writing the data to disk, if our program then writes to the disk during this period, our program will block waiting for Fsys to finish writing. Why does it not cache again?
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| Solution |
The '-a' option forces Fsys to do all of the work for each transaction, which means updating the bitmap, directory entries, etc. This means Fsys will take a little more time cleaning up after each write. Usually, the updating of the filesystem does not occur unless Fsys has nothing else to do (hence caches these things until ready), but the '-a' option forces Fsys to asynchronously write.
If a process is writing at the same priority, then it will have to wait its turn, which means blocking on Fsys until it is ready to service your process. Essentially, the cache is being bypassed which decreases performance. |
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