fs_cache_hit.sh

#! /usr/bin/env stap
global total_bytes, disk_bytes, counter

probe vfs.read.return {
    if (bytes_read>0) {
        if (devname=="N/A") {
        } else {
            total_bytes += bytes_read
        }   
    }   
}

probe ioblock.request
{
    if (rw == 0 && size > 0)
    {   
        if (devname=="N/A") { 
        } else {
            disk_bytes += size
        }   
    }   

}

# print VFS hits and misses every 5 second, plus the hit rate in %
probe timer.s(5) {
    if (counter%15 == 0) {
        printf ("\n%18s %18s %10s %10s\n", 
                "Cache Reads (KB)", "Disk Reads (KB)", "Miss Rate", "Hit Rate")
    }   
    cache_bytes = total_bytes - disk_bytes
        if (cache_bytes < 0)
            cache_bytes = 0 
                counter++
                hitrate =  10000 * cache_bytes / (cache_bytes+disk_bytes)
                missrate = 10000 * disk_bytes / (cache_bytes+disk_bytes)
                printf ("%18d %18d %6d.%02d%% %6d.%02d%%\n",
                        cache_bytes/1024, disk_bytes/1024,
                        missrate/100, missrate%100, hitrate/100, hitrate%100)
                total_bytes = 0 
                disk_bytes = 0 
}