* Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx> [2010-09-23 15:48:01]: > Currently tools like "top" gather the task information by reading procfs > files. This has several disadvantages: > > * It is very CPU intensive, because a lot of system calls (readdir, open, > read, close) are necessary. > * No real task snapshot can be provided, because while the procfs files are > read the system continues running. > * The procfs times granularity is restricted to jiffies. > > In parallel to procfs there exists the taskstats binary interface that uses > netlink sockets as transport mechanism to deliver task information to > user space. There exists a taskstats command "TASKSTATS_CMD_ATTR_PID" > to get task information for a given PID. This command can already be used for > tools like top, but has also several disadvantages: > > * You first have to find out which PIDs are available in the system. Currently > we have to use procfs again to do this. > * For each task two system calls have to be issued (First send the command and > then receive the reply). > * No snapshot mechanism is available. > > GOALS OF THIS PATCH SET > ----------------------- > The intention of this patch set is to provide better support for tools like > top. The goal is to: > > * provide a task snapshot mechanism where we can get a consistent view of > all running tasks. > * provide a transport mechanism that does not require a lot of system calls > and that allows implementing low CPU overhead task monitoring. > * provide microsecond CPU time granularity. > Looks like a good set of goals > FIRST RESULTS > ------------- > Together with this kernel patch set also user space code for a new top > utility (ptop) is provided that exploits the new kernel infrastructure. See > patch 10 for more details. > > TEST1: System with many sleeping tasks > > for ((i=0; i < 1000; i++)) > do > sleep 1000000 & > done > > # ptop_new_proc > > VVVV > pid user sys ste total Name > (#) (%) (%) (%) (%) (str) > 541 0.37 2.39 0.10 2.87 top > 3743 0.03 0.05 0.00 0.07 ptop_new_proc > ^^^^ > > Compared to the old top command that has to scan more than 1000 proc > directories the new ptop consumes much less CPU time (0.05% system time > on my s390 system).a This is very nice! > > TEST2: Show snapshot consistency with system that is 100% busy > > System with 3 CPUs: > > for ((i=0; i < $(cat /proc/cpuinfo | grep "^processor" | wc -l); i++)) > do > ./loop & > done > > # ptop_snap_proc > > VVVV VVV VVV VVVVV > pid user sys ste cuser csys cste delay total Elap+ Name > (#) (%) (%) (%) (%) (%) (%) (%) (%) (hm) (str) > 23891 99.84 0.06 0.09 0.00 0.00 0.00 0.01 99.99 0:00 loop > 23881 99.66 0.06 0.09 0.00 0.00 0.00 0.20 99.81 0:00 loop > 23886 99.65 0.06 0.09 0.00 0.00 0.00 0.20 99.80 0:00 loop > 2413 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 4:17 sshd > ... > V:V:S 299.36 0.36 0.27 0.00 0.00 0.00 0.40 300.00 4:22 > ^^^^^^ > > With the snapshot mechanism the sum of all tasks CPU times (user + system + > steal) will be exactly 300.00% CPU time with this testcase. Using > ptop_snap_proc (see patch 10) this works fine on s390. > > PATCHSET OVERVIEW > ----------------- > The code is not final and still has a few TODOs. But it is good enough for a > first round of review. The following kernel patches are provided: > > [01] Prepare-0: Use real microsecond granularity for taskstats CPU times. > [02] Prepare-1: Restructure taskstats.c in order to be able to add new commands > more easily. > [03] Prepare-2: Separate the finding of a task_struct by PID or TGID from > filling the taskstats. > [04] Add new command "TASKSTATS_CMD_ATTR_PIDS" to get a snapshot of multiple > tasks. > [05] Add procfs interface for taskstats commands. This allows to get a complete > and consistent snapshot with all tasks using two system calls (ioctl and > read). Transferring a snapshot of all running tasks is not possible using > the existing netlink interface, because there we have the socket buffer > size as restricting factor. > [06] Add TGID to taskstats. > [07] Add steal time per task accounting. > [08] Add cumulative CPU time (user, system and steal) to taskstats. > [09] Fix exit CPU time accounting. I'll review the patches, in more depth > > [10] Besides of the kernel patches also user space code is provided that > exploits the new kernel infrastructure. The user space code provides the > following: > 1. A proposal for a taskstats user space library: > 1.1 Based on netlink (requires libnl-devel-1.1-5) > 2.1 Based on the new /proc/taskstats interface (see [05]) I have some code for libnl based exploitation lying around, not sure if you've seen the same. > 2. A proposal for a task snapshot library based on taskstats library (1.1) > 3. A new tool "ptop" (precise top) that uses the libraries > > -- Three Cheers, Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
