IIRC, this is the type of thing they are doing, and as Jim mentioned: it improves performance because more pointers fit in a cache line, and therefor use less cache. With today's processor designs, using cache effectively can have huge performance benefits.
>>> Tom Marchant <m42tom-ibmm...@yahoo.com> 1/4/2010 10:45 AM >>> >On Sat, 2 Jan 2010 15:37:15 -0500, Jim Mulder <d10j...@us.ibm.com> wrote: >> >> I was told that compressed pointers for storage below 32GB fit >>into a smaller space, so more compressed pointers fit in a cache >>line, leading to more effective cache utilization. Performance is >>all about the caches these days. I am not a Java person. I don't >>know what a compressed pointer is. >> Just a wild guess. If all pointers are to storage on a doubleword boundary, the address can be shifted right three bits. Then you can point to any doubleword below 32 GB using an unsigned 32-bit address. How that might help performance is a mystery to me. -- Tom Marchant ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html CONFIDENTIALITY/EMAIL NOTICE: The material in this transmission contains confidential and privileged information intended only for the addressee. If you are not the intended recipient, please be advised that you have received this material in error and that any forwarding, copying, printing, distribution, use or disclosure of the material is strictly prohibited. If you have received this material in error, please (i) do not read it, (ii) reply to the sender that you received the message in error, and (iii) erase or destroy the material. Emails are not secure and can be intercepted, amended, lost or destroyed, or contain viruses. You are deemed to have accepted these risks if you communicate with us by email. Thank you. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
