Messages in this thread | | | From | Kallol Biswas <> | Subject | RE: process starvation with 2.6 scheduler | Date | Tue, 6 Jun 2006 10:55:44 -0700 |
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I have verified that the starved tasks are in the runqueue (prio_array_t array[0], active points to array[0]), the timestamp and last_ran indicate that they have not run for a while.
The network traffic is of request response type.
Client (on an external box)3 ports ---- 3 cables ----3 ports Emulated Host The netperf clients run on an external box, the emulated host (ppc440) runs the servers. A client sends request to a server, the server returns the reply, then the next request from the client goes to the server. There are 3 clients and 3 servers, one client-server pair for each connection (3 connections: 3 ports on external box --3 connection -- 3 ports on emulated host).
Since traffic is of request/response in nature and the packets reach user space (to netserver) before turning around I do not think slow CPU is an issue.
-----Original Message----- From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Stephen Hemminger Sent: Tuesday, June 06, 2006 9:56 AM To: linux-kernel@vger.kernel.org Subject: Re: process starvation with 2.6 scheduler
On Tue, 06 Jun 2006 10:01:58 +0200 Mike Galbraith <efault@gmx.de> wrote:
> (please line wrap) > > On Mon, 2006-06-05 at 12:48 -0700, Kallol Biswas wrote: > > Hello, > > We have a process starvation problem with our 2.6.11 kernel running on a ppc-440 based system. > > > > We have a storage SOC based on PPC-440. The SOC is emulated on a system emulator called Palladium. It is from Cadence. The system runs at 400KHz speed. It has three Ethernet ports; they are connected to outside lab network with a speed bridge. > > > > The netperf server netserver runs on the emulated system (2.6.11 kernel on Palladium). There are netperf linux clients running on a x86 box. > > > > If netperf request response (TCP_RR) traffic is run on all three ports; after sometime only one port remains active, the application (netperf client) on other two ports wait for a long time and eventually time out. > > > > The netserver code has been instrumented. For one of the starved netserver processes it has been found that the TCP_RR request from the netperf client on linux x86 box has been received by the server, it has issued send() call to send back reply but send() never returns. > > > > With an ICE connected to the Palladium (emulator) I have dumped the kernel data structures of the starved process and the active process. > > > > > > For Active Process: > > Time_slice 84 > > Policy : SCHED_NORMAL > > Dynamic priority: 118 > > Static priority: 120 > > Preempt_count: 0x20100 > > Flags = 0 > > State = 0 (TASK_RUNNING) > > > > For Starved Process: > > Time slice: 77 > > Policy: SCHED_NORMAL > > Dynamic priority: 120 > > Static priority: 120 > > Preempt_count: 0x10000000 (PREEMPT_ACTIVE is set) > > Flags = 0 > > State = 0 (TASK_RUNNING) > > > > Any help to debug the problem is welcome. > > I'm having difficulty understanding. Are you saying that the "starved" > tasks are runnable, but receiving _zero_ cpu? That's impossible with > only one other SCHED_NORMAL task afaik, which makes me think you may > mean they're not receiving cpu frequently enough to keep clients from > timing out? One task which has slept enough to acquire interactive > status (as above) can hold others off the cpu for quite a while if it > starts a burst of heavy cpu burning. If your netperf clients are > choking on this latency, running the servers at nice 19 should prevent > the problem. >
Is the processor getting consumed by network traffic in soft irq? If you are using non NAPI device driver, then it is easy to get soft irq overwhelmed with packets. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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