On 01/09/2019 12:23 PM, Waiman Long wrote: > After skipping the percpu summation of non-active IRQs on a 4-socket > Broadwell system with about 3k IRQs, about half of the CPU cycles were > spent in the kstat_irqs() call. The majority of which were used to look > up the IRQ descriptors for the corresponding IRQ numbers. > > We can recoup a lot of those lost cycles by calling kstat_irqs_usr() > only for those IRQs that are active. A bitmap is now used to keep track > of the list of the active IRQs. Changes in nr_active_irqs count will > cause the code to rescan all the IRQs and repopulate the bitmap. > > On the same 4-socket server, the introduction of this patch further > reduces the system time of reading /proc/stat 5k times from 8.048s > to 5.817s. This is a another time reduction of 28%. > > Signed-off-by: Waiman Long <[email protected]> > --- > fs/proc/stat.c | 84 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 84 insertions(+) > > diff --git a/fs/proc/stat.c b/fs/proc/stat.c > index 4b06f1b..5e2a398 100644 > --- a/fs/proc/stat.c > +++ b/fs/proc/stat.c > @@ -93,6 +93,25 @@ static u64 compute_stat_irqs_sum(void) > } > > /* > + * Write the given number of space separated '0' into the sequence file. > + */ > +static void write_zeros(struct seq_file *p, int cnt) > +{ > + /* String of 16 '0's */ > + static const char zeros[] = " 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0"; > + > + while (cnt > 0) { > + if (cnt >= 16) { > + seq_write(p, zeros, 32); > + cnt -= 16; > + } else { > + seq_write(p, zeros, 2 * cnt); > + cnt = 0; > + } > + } > +} > + > +/* > * Print out the "intr" line of /proc/stat. > */ > static void show_stat_irqs(struct seq_file *p) > @@ -100,9 +119,74 @@ static void show_stat_irqs(struct seq_file *p) > int i; > > seq_put_decimal_ull(p, "intr ", compute_stat_irqs_sum()); > + > + if (IS_ENABLED(CONFIG_SMP) && (nr_cpu_ids >= 10) && (nr_irqs >= 256)) { > + /* > + * On systems with 10 or more CPUs and 256 or more IRQs, > + * we used a bitmap to keep track of the number of active > + * IRQs and call kstat_irqs_usr() only for those IRQs. > + * The bitmap will be refreshed whenever nr_active_irqs > + * changes. > + */ > + extern atomic_t nr_active_irqs; > + static DEFINE_MUTEX(irqs_mutex); > + static int last_irq = -1; > + static int bitmap_size, active_irqs; > + static unsigned long *bitmap; > + int current_irqs = atomic_read(&nr_active_irqs); > + > + mutex_lock(&irqs_mutex); > + if (current_irqs != active_irqs) { > + /* > + * Rescan all the IRQs for active ones. > + */ > + if (nr_irqs > bitmap_size) { > + static unsigned long *new_bitmap; > + static int new_size; > + > + new_size = BITS_TO_LONGS(nr_irqs)*sizeof(long); > + new_bitmap = (unsigned long *)krealloc(bitmap, > + new_size, GFP_KERNEL); > + if (!new_bitmap) > + goto fallback; > + bitmap = new_bitmap; > + bitmap_size = new_size; > + } > + memset(bitmap, 0, bitmap_size/BITS_PER_BYTE); > + last_irq = 0;
Sorry, last_irq should be initialized to -1 here. Cheers, Longman
