On Mon, 17 Dec 2007 13:53:23 -0800 "H. Peter Anvin" <hpa@xxxxxxxxx> wrote: > When the conversion factor between jiffies and milli- or microseconds > is not a single multiply or divide, as for the case of HZ == 300, we > currently do a multiply followed by a divide. The intervening > result, however, is subject to overflows, especially since the > fraction is not simplified (for HZ == 300, we multiply by 300 and > divide by 1000). > > This is exposed to the user when passing a large timeout to poll(), > for example. > > This patch replaces the multiply-divide with a reciprocal > multiplication on 32-bit platforms. When the input is an unsigned > long, there is no portable way to do this on 64-bit platforms there is > no portable way to do this since it requires a 128-bit intermediate > result (which gcc does support on 64-bit platforms but may generate > libgcc calls, e.g. on 64-bit s390), but since the output is a 32-bit > integer in the cases affected, just simplify the multiply-divide > (*3/10 instead of *300/1000). alpha allmodconfig: kernel/time.c: In function 'jiffies_to_msecs': kernel/time.c:248: error: 'HZ_TO_MSEC_NUM' undeclared (first use in this function) kernel/time.c:248: error: (Each undeclared identifier is reported only once kernel/time.c:248: error: for each function it appears in.) kernel/time.c:248: error: 'HZ_TO_MSEC_DEN' undeclared (first use in this function) kernel/time.c: In function 'jiffies_to_usecs': kernel/time.c:264: error: 'HZ_TO_USEC_NUM' undeclared (first use in this function) kernel/time.c:264: error: 'HZ_TO_USEC_DEN' undeclared (first use in this function) kernel/time.c: In function 'usecs_to_jiffies': kernel/time.c:486: error: 'm' undeclared (first use in this function) kernel/time.c:489: warning: control reaches end of non-void function kernel/time.c: In function 'jiffies_to_usecs': kernel/time.c:267: warning: control reaches end of non-void function kernel/time.c: In function 'jiffies_to_msecs': kernel/time.c:251: warning: control reaches end of non-void function - To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
