AVOIDING NON-POSTED REQUEST DEADLOCKS IN DEVICES

• US 20120311213A1
• Filed: 04/20/2012
• Published: 12/06/2012
• Est. Priority Date: 06/01/2011
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Bender, Carl A., Hanscom, Jeffrey C., Needham, Thomas D.
• Granted Patent: US 8,516,177 B2
• Time in Patent Office: Days
• US Class Current: 710/113
• CPC Class Codes: G06F 13/364 using independent requests or grants, e.g. using separated request and grant lines

Abstract

Processing within a device is controlled in order to avoid a deadlock situation. A local request engine of the device determines prior to making a request whether the port of the device that is to service the request is making forward progress in processing other requests. If forward progress is being made, then the request is forwarded to the port. Otherwise, the request is held. This avoids a deadlock situation and allows the device to remain operative even in partial recovery situations.

Claims

1. A method of controlling processing within a device of a communications environment, the method comprising:

determining by a requester of the device whether a port of the device is able to make forward progress on inbound requests;

based on determining forward progress is blocked on the port, holding sending a request to the port; and

based on determining the port is making forward progress, sending the request to the port.

2. The method of claim 1, wherein the determining comprises checking a forward progress indicator stored within the port to determine if the port is making forward progress.

3. The method of claim 2, further comprising setting the forward progress indicator to indicate whether forward progress is being made.

4. The method of claim 3, wherein the setting the forward progress indicator comprises:

comparing a number of posted credits for the port with a threshold level; and

setting the forward progress indicator to indicate forward progress, based on the comparing indicating the number of posted credits is at a defined level with respect to the threshold level.

5. The method of claim 4, further comprising setting the forwarded progress indicator to indicate blocked, based on the comparing indicating the number of posted credits is not at the defined level with respect to the threshold level.

6. The method of claim 3, wherein the setting comprises:

determining whether at least one posted credit is outstanding for the port;

based on determining at least one posted credit is outstanding, performing one or more checks of the at least one posted credit; and

setting the forward progress indicator to indicate blocked, based on the performing indicating an insufficient number of posted credits.

7. The method of claim 6, wherein the performing comprises:

determining whether a number of the posted credits is below a threshold level; and

based on the number of the posted credits being below the threshold level, determining whether one or more posted credits were returned within a timer window, wherein the forward progress indicator is set to blocked, based on the number of posted credits being below the threshold level and one or more posted credits not being returned within the timer window.

8. The method of claim 7, further comprising setting or adjusting at least one of the threshold level and the timer window.

9. The method of claim 1, wherein the port is a south port of the device, and the requester is one of a local processor of the device or a direct memory access engine of the device.

10. The method of claim 1, wherein based on determining forward progress is blocked, the request engine performing other work.