I had the pleasure of spending a significant amount of time at the most
recent LPC with Mathieu Desnoyers and Paul McKenney. In discussing
RCU semantics in relation to epoch reclamation, it was argued that
epoch reclamation is a specialisation of RCU (rather than a generalization).
In light of this discussion, I thought it would make more sense to not expose
write-side synchronization semantics aside from ck_epoch_call (similar to
RCU call), ck_epoch_poll (identical to tick), ck_epoch_barrier and
ck_epoch_synchronization (similar to ck_epoch_synchronization). Writers will
now longer have to use write-side epoch sections but can instead rely on
epoch_barrier/synchronization for blocking semantics and ck_epoch_poll
for old tick semantics.
One advantage of this is we can avoid write-side recursion for certain workloads.
Additionally, for infrequent writes, epoch_barrier and epoch_synchronization both
allow for blocking semantics to be used so you don't have to pay the cost of
epoch_entry for non-blocking dispatch.
Example usage:
e = stack_pop(mystack);
ck_epoch_synchronize(...);
free(e);
read_begin and read_end has been replaced with ck_epoch_begin and ck_epoch_end.
If multiple writers need SMR guarantees, then they can also use ck_epoch_begin
and ck_epoch_end. Any dispatch in presence of multiple writers should be done
with-in an epoch section (for now).
There are some follow-up commits to come.
build:
- configure step will generate relevant CFLAGS.
- build profiles are for convenience (developers can use themu
for cross-compilation).
regressions:
- Renamed ck_barrier unit tests to work-around behavior
of Solaris linker.
- Adopted use of a PTHREAD_CFLAGS variable.
ck_cc:
- Added internal CK_CC_IMM macro for compilers that are
verbose against impossible inline constraints (or limited
optimizers).
ck_pr/x86*:
- Adopted CK_CC_IMM macro.
- Dropped redundant constraints.
This work was mostly completed by Theo Schlossnagle
<jesus@omniti.com>, much thanks to him. He has
also provided access to a machine with Sun Studio 12.
David Joseph
Samy Al Bahra
Samy Al Bahra
sbahra