HMB Random and Sequential Access Coherency Approach
Read commands and write commands are issued by a data storage device, but sometimes a read command can begin execution prior to the data for the write command having been written to the memory device (or HMB DRAM). In such a scenario, the data for the read command is not in the memory device, but rather, is in cache waiting to be written to the memory device in a write cache operation. In order to ensure the correct data is read, the cache write operation can be paused so that the data can be retrieved from cache rather than the memory device. Alternatively, a placeholder can be used for the read command until the write cache operation has occurred.
1 . A data storage device, comprising:
a memory device; and
a controller coupled to the memory device, wherein the controller is configured to:
initiate a read command to a direct memory access (DMA) module;
pause writing to the memory device from a cache;
retrieve data associated with the read command from cache; and
return the retrieved data as read data of the read command.
2 . The data storage device of claim 1 , wherein the cache is a host memory buffer (HMB).
3 . The data storage device of claim 1 , wherein the data storage device does not include dynamic random access memory (DRAM).
4 . The data storage device of claim 1 , wherein the controller is configured to read data from the memory device and substitute the read data with the retrieved data.
5 . The data storage device of claim 1 , wherein the DMA is configured to request the cache to pause writing.
6 . The data storage device of claim 5 , wherein the controller is configured to:
scan overlapping lines in the cache in response to the request;
reply to the DMA that the pause has occurred; and
generate a sorted list of address and data from the overlapping lines.
7 . The data storage device of claim 6 , wherein the controller is configured to determine whether the sorted list is empty.
8 . The data storage device of claim 7 , wherein in response to determining that the sorted list is not empty, provide a head of the sorted list to the DMA.
9 . The data storage device of claim 8 , wherein the DMA is configured to:
perform a read from the memory device; and
determine whether data associated with the read from the memory device belongs to a same address as the head of the sorted list.
10 . The data storage device of claim 9 , wherein the DMA is configured to:
replace the data associated with the read from the memory device with the data from the sorted list; and
return the data from the sorted list to a destination that instructed the read command.
11 . The data storage device of claim 10 , wherein the controller is configured to pop the data from the sorted list from the sorted list.
12 . A data storage device, comprising:
a memory device; and
a controller coupled to the memory device, wherein the controller is configured to:
pause a cache operation of writing data to the memory device;
substitute data from the memory device with data from the cache; and
resume the cache operation after the substituting.
13 . The data storage device of claim 12 , wherein short accesses utilize cache.
14 . The data storage device of claim 13 , wherein input/output (I/O) operations utilize DMA.
15 . The data storage device of claim 14 , wherein short accesses include physical region page (PRP), scatter gather list (SGL), submission queues (SQ), and completion queues (CQ).
16 . The data storage device of claim 15 , wherein the short accesses are through a controller memory buffer (CMB) controller.
17 . The data storage device of claim 12 , wherein the controller is configured to:
generate a sorted list of address plus data from overlapping lines in cache;
provide the sorted list to DMA;
determine that data associated with a read command is in the sorted list; and
perform the substituting based upon the determining.
18 . A data storage device, comprising:
means for storing data; and
a controller coupled to the means for storing data, wherein the controller is configured to:
initiate a read command;
determine that an address associated with the read command overlaps with an address in cache;
prioritize a direct memory access (DMA) operation over a cache read operation; and
execute the read command using data from the cache and not from the means for storing data.
19 . The data storage device of claim 18 , wherein the controller is configured to:
read data for a first address associated with the read command from the means for storing data;
skip reading data for a second address associated with the read command from the means for storing data; and
read data for a third address associated with the read command from the means for storing data.
20 . The data storage device of claim 19 , wherein the controller is configured to:
return the data associated with the first address;
insert a placeholder for data associated with the second address;
return data associated with the third address;
retrieve data associated with the second address;
replace the placeholder with the data associated with the second address;
deliver the data associated with the first address;
deliver the data associated with the second address; and
deliver the data associated with the third address after delivering the data associated with the second address.