NDIRTY cache line lookahead

A cache architecture including cache line lookahead to facilitate cache export, comprising:

• (a) a cache organized into cache lines with one or more data blocks, where each cache line has associated with it at least one dirty indication indicating whether the cache line contains dirty data;
• (b) N-line lookahead means for indicating, for each of at least M of the cache lines, whether any of the N successive cache lines contains dirty data;
• and
• (b) array sequencing means for controlling, in response to an export command, the sequence for scanning cache lines to determine, for each cache line, whether it contains dirty data, such that, if it does, such dirty data is exported;
• (d) in response to the export command, when the array sequencing means scans one of the M cache lines as determined by a current scan count, it contemporaneously accesses the N-line lookahead means to determine for such cache line whether any of the N successive cache lines contains dirty data;
• and
• (e) in response to accessing the N-line lookahead array, the array sequencing means increments the current scan count to the next cache line containing dirty data, or if none of the next N successive cache lines contains dirty data, then the array sequencing means increments the current scan count by N+1.

A cache line lookahead method for facilitating cache export in a cache organized into cache lines with one or more data blocks, where each cache line has associated with it at least one dirty indication indicating whether the cache line contains dirty data, comprising the steps:

• (a) indicating, for each of at least M of the cache lines, whether any of the N successive cache lines contains dirty data;
• (b) in response to an export command, scanning cache lines to determine, for each cache line, whether it contains dirty data, and if it does, exporting such dirty data;
• (c) when one of the M cache lines is scanned as determined by a current scan count, contemporaneously determining for such cache line whether any of the N successive cache lines contains dirty data;
• and
• (e) incrementing the current scan count to the next cache line containing dirty data, or if none of the next N successive cache lines contains dirty data, then incrementing the current scan count by N+1.

A computer system including a processor and a cache including cache line lookahead to facilitate cache export, comprising:

• (a) a system memory for storing data, the computer system using cache export operations to maintain coherency between the system memory and the cache, wherein under selected conditions dirty data is exported from the cache to the system memory;
• (b) the cache being organized into cache lines with one or more data blocks, where each cache line has associated with it at least one dirty indication indicating whether the cache line contains dirty data;
• (c) N-line lookahead means for indicating, for each of at least M of the cache lines, whether any of the N successive cache lines contains dirty data;
• and
• (d) array sequencing means for controlling, in response to an export command, the sequence for scanning cache lines to determine, for each cache line, whether it contains dirty data, such that, if it does, such dirty data is exported;
• (e) in response to the export command, when the array sequencing means scans one of the M cache lines as determined by a current scan count, it contemporaneously accesses the N-line lookahead means to determine for such cache line whether any of the N successive cache lines contains dirty data;
• and
• (f) in response to accessing the N-line lookahead array, the array sequencing means increments the current scan count to the next cache line containing dirty data, or if none of the next N successive cache lines contains dirty data, then the array sequencing means increments the current scan count by N+1.

A method of cache line lookahead to facilitate cache export operations in a computer system that includes a processor and a cache organized into cache lines with one or more data blocks, where each cache line has associated with it at least one dirty indication indicating whether the cache line contains dirty data, comprising the steps:

• (a) maintaining coherency between the cache and a system memory by exporting, under selected conditions, dirty data from the cache to the system memory;
• (b) indicating, for each of at least M of the cache lines, whether any of the N successive cache lines contains dirty data;
• (b) in response to an export command, scanning cache lines to determine, for each cache line, whether it contains dirty data, and if it does, exporting such dirty data;
• (c) when one of the M cache lines is scanned as determined by a current scan count, contemporaneously determining for such cache line whether any of the N successive cache lines contains dirty data;
• and
• (e) incrementing the current scan count to the next cache line containing dirty data, or if none of the next N successive cache lines contains dirty data, then incrementing the current scan count by N+1.