Speculative cache line write backs to avoid hotspots
First Claim
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1. A cache system comprising:
- a data cache memory comprising a plurality of cache lines;
a tag store having an entry representing each line in the cache memory wherein each entry comprises tag information for accessing the data cache, the tag information including state information indicating whether the represented cache line includes dirty data; and
a speculative write back unit monitoring the state information and operative to initiate a write back of a cache line having more than a preselected amount of dirty data while maintaining the data in the cache line and updating the state information to indicate the represented cache line has non-dirty data.
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Abstract
A cache system including a data cache memory comprising a plurality of cache lines. A tag store has an entry representing each line in the cache memory where each entry comprises tag information for accessing the data cache. The tag information includes state information indicating whether the represented cache line includes dirty data. A speculative write back unit monitors the state information and is operative to initiate a write back of a cache line having more than a preselected amount of dirty data.
123 Citations
21 Claims
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1. A cache system comprising:
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a data cache memory comprising a plurality of cache lines; a tag store having an entry representing each line in the cache memory wherein each entry comprises tag information for accessing the data cache, the tag information including state information indicating whether the represented cache line includes dirty data; and a speculative write back unit monitoring the state information and operative to initiate a write back of a cache line having more than a preselected amount of dirty data while maintaining the data in the cache line and updating the state information to indicate the represented cache line has non-dirty data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A computer system comprising:
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a processor formed as an integrated circuit chip; a cache system coupled to the processor, the cache system further comprising; an on-chip cache comprising a plurality of cache lines; a first on-chip tag store holding tag information for accessing the on-chip cache; an off-chip sub-blocked data cache comprising a plurality of cache lines wherein each cache line in the off-chip data cache corresponds to a plurality of lines in the on-chip cache; a second on-chip tag array holding tag information for accessing the off-chip data cache; a replacement mechanism monitoring the tag information in the second on-chip tag array to initiate write back of selected LRU cache lines on a least recently used basis; and a speculative write back unit monitoring the tag information in the second on-chip tag array to initiate speculative write back of selected cache lines based upon the quantity of dirty data in the selected cache lines while maintaining the data in the cache line and updating the tag information to indicate the selected cache line has non-dirty data. - View Dependent Claims (14, 15, 16, 17)
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13. The cache system of claim 13 wherein the speculative write back unit is operative to initiate a write back of a selected cache line independent of frequency with which the selected cache line is accessed.
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18. In a processor that executes coded instructions, a method for operation of a cache memory having a cache tag array comprising a plurality of entries wherein each entry stores tag information representing a line of data in the cache memory, the method comprising the steps of:
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providing state information in the tag information indicating state of the represented cache line; generating cache system access requests, each access request comprising an address identifying a memory location having data that is a target of the access; performing a cache tag lookup by applying the address in an access to the cache tag array; in response to the cache tag lookup, monitoring the state information of the cache tag entry corresponding to the access request to detect dirty data included in the represented cache line; and initiating, in response to the monitoring step, a write back of the represented cache lines including more than a preselected amount of dirty data while maintaining the data in the represented cache lines and updating the state information to indicate the represented cache lines have non-dirty data. - View Dependent Claims (19, 20, 21)
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Specification