Modify bget so that succesful lookups don't need to - acquire bcache.lock. The challenge is - concurrent brelse, which modify the list that bget - traverses. (Hint: there is no need for bget to use the - list.) + +
Several processes reading different files repeatedly will + bottleneck in the buffer cache, bcache, in bio.c. Replace the + acquire in bget with +
+ while(!tryacquire(&bcache.lock)) {
+ printf("!");
+ }
+
+
+ and run test0 from bcachetest and you will see "!"s.
+
+Modify bget so that a lookup for a buffer that is in the + bcache doesn't need to acquire bcache.lock. This more + tricky than the kalloc assignment, because bcache buffers are truly + shared among processes. You must maintain the invariant that a + buffer is only once in memory. + +
There are several races that bcache.lock protects +against, including: +
A challenge is testing whether you code is still correct. One way + to do is to artificially delay certain operations + using sleepticks. + +
Here are some hints: +