Messages in this thread | | | From | "Hunter, Jon" <> | Date | Mon, 26 Jan 2009 12:23:37 -0600 | Subject | RE: [RFC] Dynamic Tick and Deferrable Timer Support |
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Andrew Morton <mailto:akpm@linux-foundation.org> wrote on Thursday, January 15, 2009 12:16 AM:
> Venki, could you please take a look?
Andrew, Venki, if it helps here are some more details.
The function "__next_timer_interrupt()" (in file kernel/timer.c) consists of two main loops. The first loop (shown below) looks for timer events in tv1.
898 /* Look for timer events in tv1. */ 899 index = slot = timer_jiffies & TVR_MASK; 900 do { 901 list_for_each_entry(nte, base->tv1.vec + slot, entry) { 902 if (tbase_get_deferrable(nte->base)) 903 continue; 904 905 found = 1; 906 expires = nte->expires; 907 /* Look at the cascade bucket(s)? */ 908 if (!index || slot < index) 909 goto cascade; 910 return expires; 911 } 912 slot = (slot + 1) & TVR_MASK; 913 } while (slot != index);
You can see from the above code snippet, that if a timer event is found for tv1, then it performs a test to see if this timer event is deferrable (lines 902 and 903). If no timer events are found for tv1, then the code enters a second loop, a for-loop with a nested do-while loop, that looks for timer events in tv2-tv5.
927 for (array = 0; array < 4; array++) { 928 struct tvec *varp = varray[array]; 929 930 index = slot = timer_jiffies & TVN_MASK; 931 do { 932 list_for_each_entry(nte, varp->vec + slot, entry) { 933 found = 1; 934 if (time_before(nte->expires, expires)) 935 expires = nte->expires; 936 } 937 /* 938 * Do we still search for the first timer or are 939 * we looking up the cascade buckets ? 940 */ 941 if (found) { 942 /* Look at the cascade bucket(s)? */ 943 if (!index || slot < index) 944 break; 945 return expires; 946 } 947 slot = (slot + 1) & TVN_MASK; 948 } while (slot != index); 949 950 if (index) 951 timer_jiffies += TVN_SIZE - index; 952 timer_jiffies >>= TVN_BITS; 953 }
In the above code, you will see that if a timer event is found there is no test to see if this timer event is deferrable. The patch that I proposed simply adds two lines of code that performs the same test as seen in the tv1 loop to check if a timer is deferrable for tv2-tv5. In other words, add lines 902 and 903, in between lines 932 and 933 in the function __next_timer_interrupt().
Cheers Jon
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