Multiprocessor system including a cache memory with tag copy units

• US 5,375,220 A
• Filed: 06/30/1992
• Issued: 12/20/1994
• Est. Priority Date: 07/04/1991
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Ishikawa, Tadashi
• Primary Examiner(s): Gossage, Glenn
• Application Number:
  US07/906,502
• Time in Patent Office: 903 Days
• Field of Search: 395/425, 395/400
• US Class Current: 711/141
• CPC Class Codes: G06F 12/0822 Copy directories local copy tags for implementing a bus snooping protocol G06F12/0831

Abstract

A multiprocessor computer system includes main memories and processors which are connected through a crossbar switching network, and a tag copying mechanism having copies of tags of caches of the processors connected to each main memory. When each of the main memories is updated, a corresponding tag copy is checked to discriminate whether or not an updating request hits the cache having an original tag. Upon detection of a hit, a cancel or invalidate request is sent to the processor which corresponds to the hit cache, and which is not a main memory updating request source, thereby invalidating the corresponding cache line of the cache of that processor.

Claims

1. A multiprocessor computer system comprising:

a) first memory means for storing data, a first part of a logical address space of the computer system being assigned to the first memory means;

b) second memory means for storing data, a second part of the logical address space of the computer system being assigned to the second memory means;

c) first processor means, which is accessible to either of the first and second parts of the logical address space, for performing a processor operation using the logical address space;

d) second processor means, which is accessible to either of the first and second parts of the logical address space, for performing a processor operation using the logical address space;

e) first cache means for, when said first processor means accesses one of said first and second memory means, holding data transferred by an access between said first processor means and one of said first and second memory means, and holding first tag information showing an address to be allocated to the transferred data;

f) second cache means for, when said second processor means accesses one of said first and second memory means, holding data transferred by an access between said second processor means and one of said first and second memory means, and holding second tag information showing an address to be allocated to the transferred data;

g) selectively connecting means for selectively connecting said first processor means to one or both of said first and second memory means, and selectively connecting said second processor means to one or both of said first and second memory means;

h) first tag copying means, coupled to a node between said selectively connecting means and said first memory means, for holding a copy of each of the first and second tag information;

i) second tag copying means, coupled to a node between said selectively connecting means and said second memory means, for holding a copy of each of the first and second tag information;

j) first cache control means, when it is determined from the first tag information held in said first tag copying means that, due to the access to said first memory means, by said second processor means a content of the accessed logical address space differs from a content of said first cache means, for preventing said first processor means from using the content of said first cache means; and

k) second cache control means, when it is determined from the second tag information held in said second tag copying means that, due to the access to said second memory means by said first processor means, a content of the accessed logical address differs from a content of said second cache means, for preventing said second processor means from using the content of said second cache means.

2. A system according to claim 1, wherein said first cache control means includes:

A tag copy means, coupled to said first memory means, for storing a copy of an address part of the first tag information;

A tag comparison means for comparing address information of the address accessed by said second processor means with the address part stored in said A tag copy means so as to generate a first signal when the address information corresponds to the address part; and

means for invalidating the held by said first cache means first tag information when said A tag comparison means generates the first signal, said second processor means performs a writing access to said first or second memory means.

3. A system according to claim 1, wherein said first processor means supplies said first cache means with first processor information serving to identify said first processor means when said first processor means accesses the logical address space, and said first cache control means includes:

A tag copy means, coupled to said first memory means, for storing a copy of an address part of the first tag information;

A tag comparison means for comparing address information of the address accessed by said second processor means with the address part stored in said A tag copy means so as to generate a first signal when the address information corresponds to the address part;

processor check means for comparing a predetermined processor information with the first processor information so that a second signal is generated when the predetermined processor information matches the first process information, and so that a third signal is generated when the predetermined processor information differs from the first processor information; and

means for invalidating the of said first cache means first tag information when said A tag comparison means generates the first signal and said processor check means generates the third signal, and if said second processor means performs a writing access to said first or second memory means.

4. A system according to claim 1, wherein said first cache control means includes:

A tag copy means, coupled to said first memory means, for storing a copy of an address part of the first tag information;

A tag comparison means for comparing address information of the address accessed by said second processor means with the address part stored in said A tag copy means so as to generate a first signal when the address information corresponds to the address part;

V tag copy means, coupled to said first memory means, for storing a copy of a valid bit portion of the first tag information so as to generate a valid signal; and

means for invalidating the of said first cache means first tag information when said A tag comparison means generates the first signal and said V tag copy means the valid signal, and if said second processor means performs a writing access to said first or second memory means.

5. A system according to claim 1, wherein said first processor means supplies said first cache means with first processor information serving to identify said first processor means when said first processor means accesses the logical address space, and said first cache control means includes:

"A" tag copy means, coupled to said first memory means, for storing a copy of an address part of the first tag information;

A tag comparison means for comparing address information of the address accessed by said second processor means with the address part stored in said A tag copy means so as to generate a first signal when the address information corresponds to the address part;

processor check means for comparing a predetermined processor information with the first processor information so that a second signal is generated when the predetermined processor information matches the first processor information and so that a third signal is generated when the predetermined processor information differs from the first processor information; and

means for copying the address part of the first tag information to said A tag copy means when said processor check means generates the second signal, and if said first processor means performs a reading access to said first or second memory means;

V tag copy means, coupled to said first memory means, for storing a copy of a valid bit portion of the first tag information so as to generate a valid signal; and

means for invalidating the of said first cache means first tag information when said A tag comparison means generates the first signal, said V tag copy means the valid signal, and said processor check means generates the third signal, and if said second processor means performs a writing access to said first or second memory means.

6. A system according to claim 1, wherein said first processor means supplies said first cache means with first processor information serving to identify said first processor means when said first processor means accesses the logical address space, and said first cache control means includes:

A tag copy means, coupled to said first memory means, for storing a copy of an address part of the first tag information;

"A" tag comparison means for comparing address information of the address accessed by said second processor means with the address part stored in said A tag copy means so as to generate a first signal when the address information corresponds to the address part;

processor check means for comparing a predetermined processor information with the first processor information so that a second signal is generated when the predetermined processor information matches the first processor information and so that a third signal is generated when the predetermined processor information differs from the first processor information; and

means for copying the address part of the first tag information to said A tag copy means when said processor check means generates the second signal, and if said first processor means performs a reading access to said first or second memory means.

7. A system according to claim 6, wherein said first cache control means further includes:

means for invalidating the of said first cache means first tag information when said A tag comparison means generates the first signal and said processor check means generates the third signal, and if said second processor means performs a writing access to said first or second memory means.