cellular-infrastructure
/
osmo-pcu
mirror of https://gerrit.osmocom.org/osmo-pcu
9
0
Fork 1
Code Issues Releases Wiki Activity

alloc: Change tx_window optimization strategy 

Currently each tx_window combination is checked only once by using a
set containing the sets of TX slots that have been checked already.
This approach does not ensure, that num_tx and ul_ts really match the
tx_window being tested. This does not make a difference with the
current test cases probably because num_tx starts with 1 and is
increased each iteration. Since the bitmap optimization is equivalent
to a cache optimization strategy that only uses tx_window as key. On
the other hand, ul_ts, num_tx, and rx_mask cannot be derived from
tx_window, but these values are also refered to after the call to
test_and_set_bit(). This makes it difficult to prove that correctness
of the caching. While this will not lead to a defect, the results
might be less optimal.

This commit changes the optimization strategy to skip all tx_window
where ul_ts and ul_ts+num_tx-1 are not both contained.  This provides
a similar degree of optimization like the set approach (only the
iteration with num_ts == 8 is not optimized, which only applies to to
ms class 18 and 29 MS) but ensures that the values of the related
variables have a clear relationship.

Note that the bitset based optimization for rx_window does not suffer
from a possible cache inconsistency, since only tx_window and
rx_window (tx_slot_count and rx_slot_count can be derived from the
windows and thus are covered by the cache key) are used after the call
to test_and_set_bit(). tx_window is constant over the whole lifetime
of the cache.

Sponsored-by: On-Waves ehf
This commit is contained in:
Jacob Erlbeck 2015-07-16 11:48:43 +02:00
parent f16a069fd7
commit e21b79cb21
1 changed files with 4 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
src/gprs_rlcmac_ts_alloc.cpp
View File

@ -481,8 +481,6 @@ static int find_multi_slots(struct gprs_rlcmac_bts *bts,
enum {MASK_TT, MASK_TR};
unsigned mask_sel;
uint32_t checked_tx[256/32] = {0};
if (ms->ms_class() >= 32) {
LOGP(DRLCMAC, LOGL_ERROR, "Multislot class %d out of range.\n",
ms->ms_class());
@ -593,11 +591,12 @@ static int find_multi_slots(struct gprs_rlcmac_bts *bts,
/* Filter out unavailable slots */
tx_window &= *ul_slots;
/* Avoid repeated TX combination check */
if (test_and_set_bit(checked_tx, tx_window))
/* Skip if the the first TS (ul_ts) is not in the set */
if ((tx_window & (1 << ul_ts)) == 0)
continue;
if (!tx_window)
/* Skip if the the last TS (ul_ts+num_tx-1) is not in the set */
if ((tx_window & (1 << ((ul_ts+num_tx-1) % 8))) == 0)
continue;
tx_slot_count = bitcount(tx_window);