Agner`s CPU blog

Software optimization resources | E-mail subscription to this blog | www.agner.org

Proposal now published
Author: Hubert Lamontagne Date: 2016-03-28 19:20
The multi level tlb looks complex, but it has fewer corner cases than having an extra adder in the address translation : you can use a physically indexed tlb in parallel with cache lookup is the same size as your cache line way - this is why CPUs with 2-way 8kb L1 (4kb per way) use 4kb MMU pages on x86!

For task switching, it's probably easier to change the master page table address (CR3 on x86) and clear the tlb than to do a real task switch. Or alternatively, you can have a tlb tagged per process and then you just need to change the page table base address + process ID register!

The way MIPS stays simple is that they disallow any sort of multi step situational thing with lots of changing registers and multiple memory accesses... No push/pop, no call/return, no automatic loading of selector offsets and segment size like on 286, and especially no task switch instruction. They even have a software tlb! That's also why it has the separate multiply result register - not for the high/low 32x32->64 thing but rather to avoid dealing with the really long latency result.

This is also why RISC-V is designed that way: the idea is that by having no multi result instructions, but having higher throughput because it's easier to make a CPU with out of order execution and lots of execution units, you still come ahead in overall speed.

Push/pop has the disadvantage of reupdating the stack pointer every time, instead of once for the whole group of loads/stores (the MIPS way). So I was suggesting dual load/store, not dual push/pop.

I think the voodoo GCC uses is that c++ specs say that overflowing integers are "undefined" - if you promote your int32s to int64 but never overflow them the result is the same!

 
thread Proposal for an ideal extensible instruction set new - Agner - 2015-12-27
replythread Itanium new - Ethan - 2015-12-28
last reply Itanium new - Agner - 2015-12-28
replythread Proposal for an ideal extensible instruction set new - hagbardCeline - 2015-12-28
last replythread Proposal for an ideal extensible instruction set new - Agner - 2015-12-28
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
replythread Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-05
replythread Proposal for an ideal extensible instruction set new - John D. McCalpin - 2016-01-05
last reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-06
last reply Proposal for an ideal extensible instruction set new - Ook - 2016-01-05
last reply Proposal for an ideal extensible instruction set new - acppcoder - 2016-03-27
reply Proposal for an ideal extensible instruction set new - Jake Stine - 2016-01-11
replythread Proposal for an ideal extensible instruction set new - Agner - 2016-01-12
last replythread Proposal for an ideal extensible instruction set new - Jonathan Morton - 2016-02-02
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-03
last replythread Proposal for an ideal extensible instruction set new - Jonathan Morton - 2016-02-12
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-18
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-21
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-22
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-23
replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-23
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-24
last replythread Proposal for an ideal extensible instruction set new - asdf - 2016-02-24
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-02-24
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-02-25
replythread limit instruction length to power of 2 new - A-11 - 2016-02-24
last replythread limit instruction length to power of 2 new - Agner - 2016-02-24
replythread Any techniques for more than 2 loads per cycle? new - Hubert Lamontagne - 2016-02-24
last reply Any techniques for more than 2 loads per cycle? new - Agner - 2016-02-25
last replythread limit instruction length to power of 2 new - A-11 - 2016-02-25
last reply limit instruction length to power of 2 new - Hubert Lamontagne - 2016-02-25
replythread More ideas new - Agner - 2016-03-04
replythread More ideas new - Hubert Lamontagne - 2016-03-07
last reply More ideas new - Agner - 2016-03-08
last reply More ideas new - Agner - 2016-03-09
replythread Proposal for an ideal extensible instruction set new - Joe Duarte - 2016-03-07
reply Proposal for an ideal extensible instruction set new - Agner - 2016-03-08
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-03-08
last replythread Proposal for an ideal extensible instruction set new - Joe Duarte - 2016-03-09
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-03-10
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-03-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-03-11
last replythread Proposal for an ideal extensible instruction set new - anon2718 - 2016-03-13
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-03-14
replythread A design without a TLB new - Agner - 2016-03-11
replythread A design without a TLB new - Hubert Lamontagne - 2016-03-11
reply A design without a TLB new - Agner - 2016-03-11
last reply A design without a TLB new - Agner - 2016-03-12
reply A design without a TLB new - Bigos - 2016-03-13
last reply A design without a TLB new - Agner - 2016-03-28
replythread Proposal now published new - Agner - 2016-03-22
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-23
last replythread Proposal now published new - Agner - 2016-03-24
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-24
last replythread Proposal now published new - Agner - 2016-03-24
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-24
last replythread Proposal now published new - Agner - 2016-03-25
last replythread Proposal now published - Hubert Lamontagne - 2016-03-28
last replythread Proposal now published new - Agner - 2016-03-29
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-30
last replythread Proposal now published new - Agner - 2016-03-30
last replythread Do we need instructions with two outputs? new - Agner - 2016-03-31
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-01
reply Do we need instructions with two outputs? new - Agner - 2016-04-01
replythread Do we need instructions with two outputs? new - Joe Duarte - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-02
last reply Do we need instructions with two outputs? new - Joe Duarte - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-02
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-03
reply Do we need instructions with two outputs? new - Joe Duarte - 2016-04-03
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-03
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-04
reply Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-04
last replythread Do we need instructions with two outputs? new - Joe Duarte - 2016-04-06
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-07
last replythread Do we need instructions with two outputs? new - HarryDev - 2016-04-08
last reply Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-09
replythread How about stack machine ISA? new - A-11 - 2016-04-10
last replythread treating stack ISA as CISC architecure new - A-11 - 2016-04-14
last replythread treating stack ISA as CISC architecure new - Agner - 2016-04-14
last replythread treating stack ISA as CISC architecure new - A-11 - 2016-04-17
replythread treating stack ISA as CISC architecure new - Hubert Lamontagne - 2016-04-17
last replythread stack ISA versus long vectors new - Agner - 2016-04-18
last replythread stack ISA versus long vectors new - Hubert Lamontagne - 2016-04-19
last reply stack ISA versus long vectors new - Agner - 2016-04-20
last reply treating stack ISA as CISC architecure new - A-11 - 2016-04-18
replythread Proposal for an ideal extensible instruction set new - zboson - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-04-12
last reply Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-04-12
replythread Version 1.01 new - Agner - 2016-05-10
last replythread Version 1.01 new - Hubert Lamontagne - 2016-05-13
last replythread Version 1.01 new - Agner - 2016-05-14
last replythread Version 1.01 new - Harry - 2016-06-02
replythread Public repository new - Agner - 2016-06-02
reply Public repository new - Harry - 2016-06-02
last reply Public repository new - Harry - 2016-06-02
last reply Public repository new - Agner - 2016-06-09
replythread Rethinking DLLs and shared objects new - Agner - 2016-05-20
replythread Rethinking DLLs and shared objects new - cv - 2016-05-20
last reply Rethinking DLLs and shared objects new - Agner - 2016-05-20
replythread Rethinking DLLs and shared objects new - Peter Cordes - 2016-05-30
last replythread Rethinking DLLs and shared objects new - Agner - 2016-05-30
last replythread Rethinking DLLs and shared objects new - Joe Duarte - 2016-06-17
last replythread Rethinking DLLs and shared objects new - Agner - 2016-06-18
last reply Rethinking DLLs and shared objects new - Bigos - 2016-06-18
last replythread Rethinking DLLs and shared objects new - Freddie Witherden - 2016-06-02
last replythread Rethinking DLLs and shared objects new - Agner - 2016-06-04
last replythread Rethinking DLLs and shared objects new - Freddie Witherden - 2016-06-04
last reply Rethinking DLLs and shared objects new - Agner - 2016-06-06
replythread Is it better to have two stacks? new - Agner - 2016-06-05
reply Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-07
replythread Is it better to have two stacks? new - Eden Segal - 2016-06-13
last replythread Is it better to have two stacks? new - Agner - 2016-06-13
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-14
last replythread Is it better to have two stacks? new - Agner - 2016-06-14
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-15
last replythread Is it better to have two stacks? new - Agner - 2016-06-15
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-16
last replythread Is it better to have two stacks? new - Agner - 2016-06-16
last reply Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-17
last reply Is it better to have two stacks? new - Freddie Witherden - 2016-06-22
last reply Now on Github new - Agner - 2016-06-26