REDUCED-OVERHEAD DMA

• US 20040172490A1
• Filed: 04/19/2004
• Published: 09/02/2004
• Est. Priority Date: 04/11/2001
• Status: Active Grant

• Current Assignee: Chelsio Communications Incorporated
• Original Assignee: Chelsio Communications Incorporated
• Inventors: Eiriksson, Asgeir Thor, Stadler, Mark, Naghshineh, Kianoosh
• Granted Patent: US 6,813,652 B2
• Time in Patent Office: Days
• US Class Current: 710/22
• CPC Class Codes: G06F 13/28 using burst mode transfer, e.g. direct memory access DMA, cycle steal G06F13/32 takes precedence

Abstract

A plurality of direct memory access data transfers are accomplished to transfer data from a host to an adaptor. For each transfer, an indication of locations of at least one group of storage locations associated with the host available to hold the data to be transferred to the host is provided from the host to the adaptor. An indication of the provided indication is maintained, for that transfer, by the host. Based on the indication of locations provided from the host to the adaptor, data is transferred to the at least one group of storage locations from the adaptor. An indication is provided from the adaptor to the host that the data transferring step has been completed with respect to the at least one group of storage locations. The host determines the locations corresponding to the at least one group of storage locations based on the indications maintained by the host and retrieving the data from the at least one group of storage locations based on the determination. A similar method is provided to transfer data from the adaptor to the host. Broadly speaking, the host and adaptor retain state information between DMA data transfers. As a result, absolute values of overhead items need not be transferred between the host CPU and the I/O device for each DMA data transfer, and the amount of overhead is reduced.

Claims

1. A method for accomplishing a plurality of direct memory access data transfers from a host to an adaptor, comprising:

for each transfer,

providing, from the host to the adaptor, an indication of locations of at least one group of storage locations associated with the host holding the data to be transferred to the adaptor;

maintaining an indication of the provided indication, for that transfer, by the host;

based on the indication of locations provided from the host to the adaptor, transferring data from the at least one group of storage locations to the adaptor;

providing, from the adaptor to the host, an indication that the data transferring step has been completed with respect to the at least one group of storage locations; and

by the host, determining the locations corresponding to the at least one group o storage locations based on the indications maintained by the host and freeing the locations of the at least one group of storage locations based on the determination.

2. The method of claim 1, further comprising:

the host maintaining a write pointer to the indications of locations maintained by the host for the plurality of transfers; and

the adaptor maintaining a read pointer to the indications of locations.

3. The method of claim 2, further comprising:

the host maintaining a shadow copy of the indications of locations write pointer.

4. The method of claim 3, further comprising:

the host maintaining the shadow copy of the indications of locations write pointer includes the host updating the shadow copy of the indications of locations write pointer, at periods greater than the periods of the data transfers.

5. The method of claim 4, further comprising:

the adaptor maintaining the indications of locations read pointer based on reading the indications of locations.

6. The method of claim 5, further comprising:

the adaptor reading the indications of locations based on a difference between the shadow copy of the indications of locations write pointer and the adaptor-maintained indications of locations read pointer.

7. The method of claim 6, wherein:

providing the indication of locations for a plurality of direct memory access data transfers includes;

storing the indications of locations into a locations indications memory associated with the host; and

performing a direct memory access read of the stored indications of locations from the locations indications memory.

8. The method of claim 7, wherein:

the storing and the direct memory access read are such that the locations indications memory is accessed in a first-in, last-out manner.

9. A method for accomplishing a plurality of direct memory access data transfers from an adaptor to host, comprising:

for each transfer,

providing, from the host to the adaptor, an indication of locations of at least one group of storage locations associated with the host available to hold the data to be transferred to the host;

maintaining an indication of the provided indication, for that transfer, by the host;

based on the indication of locations provided from the host to the adaptor, transferring data to the at least one group of storage locations from the adaptor;

providing, from the adaptor to the host, an indication that the data transferring step has been completed with respect to the at least one group of storage locations; and

by the host, determining the locations corresponding to the at least one group of storage locations based on the indications maintained by the host and retrieving the data from the at least one group of storage locations based on the determination.

10. The method of claim 9, further comprising:

the host maintaining a write pointer to the indications of locations maintained by the host for the plurality of transfers; and

the adaptor maintaining a read pointer to the indications of locations.

11. The method of claim 10, further comprising:

the host maintaining a shadow copy of the indications of locations write pointer.

12. The method of claim 11, further comprising:

the host maintaining the shadow copy of the indications of locations write pointer includes the host updating the shadow copy of the indications of locations write pointer, at periods greater than the periods of the data transfers.

13. The method of claim 12, further comprising:

the adaptor maintaining the indications of locations read pointer based on reading the indications of locations.

14. The method of claim 13, further comprising:

the adaptor reading the indications of locations based on a difference between the shadow copy of the indications of locations write pointer and the adaptor-maintained indications of locations read pointer.

15. The method of claim 14, wherein:

providing the indication of locations for a plurality of direct memory access data transfers includes;

storing the indications of locations into a locations indications memory associated with the host; and

performing a direct memory access read of the stored indications of locations from the locations indications memory.

16. The method of claim 15, wherein:

the storing and the direct memory access read are such that the locations indications memory is accessed in a first-in, last-out manner.