Overflow can occur very easily with 32 bits, e.g., with 1 second
us_idle is approx. 2^20, which leaves only 11-Wlog bits for queue
length. Since the EWMA exponent is typically around 9, queue
lengths larger than 2^2 cause overflow. Whether the affected
branch is taken when us_idle is as high as 1 second, depends on
Scell_log, but with rather reasonable configuration Scell_log is
large enough to cause p->Stab to have zero index, which always
results zero shift (typically also few other small indices result
in zero shift).
Signed-off-by: Ilpo Järvinen <[EMAIL PROTECTED]>
---
include/net/red.h | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/include/net/red.h b/include/net/red.h
index 2ed4358..cfc2625 100644
--- a/include/net/red.h
+++ b/include/net/red.h
@@ -213,7 +213,7 @@ static inline unsigned long red_calc_qav
* Seems, it is the best solution to
* problem of too coarse exponent tabulation.
*/
- us_idle = (p->qavg * us_idle) >> p->Scell_log;
+ us_idle = (p->qavg * (u64)us_idle) >> p->Scell_log;
if (us_idle < (p->qavg >> 1))
return p->qavg - us_idle;
--
1.4.0
-
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