Re: [gem5-users] Handling write backs
Hello Andreas, Now i understand. Thanks, Prathap On Mon, Jul 27, 2015 at 4:49 AM, Andreas Hansson andreas.hans...@arm.com wrote: Hi Prathap, When you write with a granularity smaller than a cache line (to your L1 D cache), the cache will read the line in exclusive state, and then write the specified part. If you write a whole line, then there is no need to first read. The latter behaviour is supported for whole-line write operations only. Andreas From: gem5-users gem5-users-boun...@gem5.org on behalf of Prathap Kolakkampadath kvprat...@gmail.com Reply-To: gem5 users mailing list gem5-users@gem5.org Date: Tuesday, 21 July 2015 23:14 To: gem5 users mailing list gem5-users@gem5.org Subject: Re: [gem5-users] Handling write backs Hello Users, I figured out that the Gem5 implements fetch-on-write-miss policy. On a write miss, allocateMissBuffer() is called to allocate an MSHR ; which send the timing request to bring this cache line. Once the request is ready, in the response path, handleFill() is called, which is responsible to insert the block in to the cache. While inserting, if the replacing victim block is dirty;a write back packet is generated and is copied to write buffers. After which satisfyCpuSideRequest() is called to write the data to the newly assigned block and marks it as dirty. Thanks, Prathap On Tue, Jul 21, 2015 at 11:21 AM, Prathap Kolakkampadath kvprat...@gmail.com wrote: Hello Users, I am using classic memory system. What is the write miss policy implemented in Gem5? Looking at the code it looks like, gem5 implements *no-fetch-on-write-miss* policy; the access() inserts a block in cache, when the request is writeback and it misses the cache. However, when i run a test with bunch of write misses, i see equal number of reads and writes to DRAM memory. This could happen if the policy is *fetch-on-write-miss.* So far i couldn't figure this out. It would be great if someone can throw some pointers to understand this further. Thanks, Prathap On Mon, Jul 20, 2015 at 2:02 PM, Prathap Kolakkampadath kvprat...@gmail.com wrote: Hello Users, I am running a test which generate write misses to LLC. I am looking at the cache implementation code. What i understood is, write are treated as write backs; on miss, write back commands allocate a new block in cache and write the data into it and marks this block as dirty. When the dirty blocks are replaced,these will be written in to write buffers. I have following questions on this: 1) When i run the test which generates write misses, i see same number of reads from memory as the number of writes. Does this mean, write backs also fetches the cache-line from main memory? 2) When the blocks in write buffers will be written to memory? Is it written when the write buffers are full? It would be great if someone can help me in understanding this. Thanks, Prathap -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England Wales, Company No: 2557590 ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England Wales, Company No: 2548782 ___ gem5-users mailing list gem5-users@gem5.org http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users ___ gem5-users mailing list gem5-users@gem5.org http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users
Re: [gem5-users] Handling write backs
Hi Prathap, When you write with a granularity smaller than a cache line (to your L1 D cache), the cache will read the line in exclusive state, and then write the specified part. If you write a whole line, then there is no need to first read. The latter behaviour is supported for whole-line write operations only. Andreas From: gem5-users gem5-users-boun...@gem5.orgmailto:gem5-users-boun...@gem5.org on behalf of Prathap Kolakkampadath kvprat...@gmail.commailto:kvprat...@gmail.com Reply-To: gem5 users mailing list gem5-users@gem5.orgmailto:gem5-users@gem5.org Date: Tuesday, 21 July 2015 23:14 To: gem5 users mailing list gem5-users@gem5.orgmailto:gem5-users@gem5.org Subject: Re: [gem5-users] Handling write backs Hello Users, I figured out that the Gem5 implements fetch-on-write-miss policy. On a write miss, allocateMissBuffer() is called to allocate an MSHR ; which send the timing request to bring this cache line. Once the request is ready, in the response path, handleFill() is called, which is responsible to insert the block in to the cache. While inserting, if the replacing victim block is dirty;a write back packet is generated and is copied to write buffers. After which satisfyCpuSideRequest() is called to write the data to the newly assigned block and marks it as dirty. Thanks, Prathap On Tue, Jul 21, 2015 at 11:21 AM, Prathap Kolakkampadath kvprat...@gmail.commailto:kvprat...@gmail.com wrote: Hello Users, I am using classic memory system. What is the write miss policy implemented in Gem5? Looking at the code it looks like, gem5 implements no-fetch-on-write-miss policy; the access() inserts a block in cache, when the request is writeback and it misses the cache. However, when i run a test with bunch of write misses, i see equal number of reads and writes to DRAM memory. This could happen if the policy is fetch-on-write-miss. So far i couldn't figure this out. It would be great if someone can throw some pointers to understand this further. Thanks, Prathap On Mon, Jul 20, 2015 at 2:02 PM, Prathap Kolakkampadath kvprat...@gmail.commailto:kvprat...@gmail.com wrote: Hello Users, I am running a test which generate write misses to LLC. I am looking at the cache implementation code. What i understood is, write are treated as write backs; on miss, write back commands allocate a new block in cache and write the data into it and marks this block as dirty. When the dirty blocks are replaced,these will be written in to write buffers. I have following questions on this: 1) When i run the test which generates write misses, i see same number of reads from memory as the number of writes. Does this mean, write backs also fetches the cache-line from main memory? 2) When the blocks in write buffers will be written to memory? Is it written when the write buffers are full? It would be great if someone can help me in understanding this. Thanks, Prathap -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England Wales, Company No: 2557590 ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in England Wales, Company No: 2548782 ___ gem5-users mailing list gem5-users@gem5.org http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users
Re: [gem5-users] Handling write backs
Hello Users, I am using classic memory system. What is the write miss policy implemented in Gem5? Looking at the code it looks like, gem5 implements *no-fetch-on-write-miss* policy; the access() inserts a block in cache, when the request is writeback and it misses the cache. However, when i run a test with bunch of write misses, i see equal number of reads and writes to DRAM memory. This could happen if the policy is *fetch-on-write-miss.* So far i couldn't figure this out. It would be great if someone can throw some pointers to understand this further. Thanks, Prathap On Mon, Jul 20, 2015 at 2:02 PM, Prathap Kolakkampadath kvprat...@gmail.com wrote: Hello Users, I am running a test which generate write misses to LLC. I am looking at the cache implementation code. What i understood is, write are treated as write backs; on miss, write back commands allocate a new block in cache and write the data into it and marks this block as dirty. When the dirty blocks are replaced,these will be written in to write buffers. I have following questions on this: 1) When i run the test which generates write misses, i see same number of reads from memory as the number of writes. Does this mean, write backs also fetches the cache-line from main memory? 2) When the blocks in write buffers will be written to memory? Is it written when the write buffers are full? It would be great if someone can help me in understanding this. Thanks, Prathap ___ gem5-users mailing list gem5-users@gem5.org http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users
Re: [gem5-users] Handling write backs
Hello Users, I figured out that the Gem5 implements fetch-on-write-miss policy. On a write miss, allocateMissBuffer() is called to allocate an MSHR ; which send the timing request to bring this cache line. Once the request is ready, in the response path, handleFill() is called, which is responsible to insert the block in to the cache. While inserting, if the replacing victim block is dirty;a write back packet is generated and is copied to write buffers. After which satisfyCpuSideRequest() is called to write the data to the newly assigned block and marks it as dirty. Thanks, Prathap On Tue, Jul 21, 2015 at 11:21 AM, Prathap Kolakkampadath kvprat...@gmail.com wrote: Hello Users, I am using classic memory system. What is the write miss policy implemented in Gem5? Looking at the code it looks like, gem5 implements *no-fetch-on-write-miss* policy; the access() inserts a block in cache, when the request is writeback and it misses the cache. However, when i run a test with bunch of write misses, i see equal number of reads and writes to DRAM memory. This could happen if the policy is *fetch-on-write-miss.* So far i couldn't figure this out. It would be great if someone can throw some pointers to understand this further. Thanks, Prathap On Mon, Jul 20, 2015 at 2:02 PM, Prathap Kolakkampadath kvprat...@gmail.com wrote: Hello Users, I am running a test which generate write misses to LLC. I am looking at the cache implementation code. What i understood is, write are treated as write backs; on miss, write back commands allocate a new block in cache and write the data into it and marks this block as dirty. When the dirty blocks are replaced,these will be written in to write buffers. I have following questions on this: 1) When i run the test which generates write misses, i see same number of reads from memory as the number of writes. Does this mean, write backs also fetches the cache-line from main memory? 2) When the blocks in write buffers will be written to memory? Is it written when the write buffers are full? It would be great if someone can help me in understanding this. Thanks, Prathap ___ gem5-users mailing list gem5-users@gem5.org http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users
[gem5-users] Handling write backs
Hello Users, I am running a test which generate write misses to LLC. I am looking at the cache implementation code. What i understood is, write are treated as write backs; on miss, write back commands allocate a new block in cache and write the data into it and marks this block as dirty. When the dirty blocks are replaced,these will be written in to write buffers. I have following questions on this: 1) When i run the test which generates write misses, i see same number of reads from memory as the number of writes. Does this mean, write backs also fetches the cache-line from main memory? 2) When the blocks in write buffers will be written to memory? Is it written when the write buffers are full? It would be great if someone can help me in understanding this. Thanks, Prathap ___ gem5-users mailing list gem5-users@gem5.org http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users
