Changes between Version 62 and Version 63 of WikiStart


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Jan 20, 2020, 2:37:14 PM (2 years ago)
Author:
alain
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    v62 v63  
    1919 * On a typical Intel-based hardware platform containing '''64-bit cores''', the physical address has 44 bits : the 4 MSB bits define the target cluster identifier, and the 40 LSB bits define the local physical address LPA. To avoid contention, the kernel code is replicated in all clusters to define one KCODE physical segment. and ALMOS-MKH uses the '''Instruction MMU''' to map - in each cluster -  the local kernel code copy in the kernel virtual space. Regarding the data accesses, each cluster contains  one KDATA and one KHEAP physical segments (the KHEAP physical segment contains all local physical memory not occupied by KCODE and KDATA). As the 48 bits virtual address space is large enough to map all these distributed KDATA[cxy] and KHEAP[cxy] segments, they can be all mapped in the kernel virtual space, and the '''Data MMU''' is used to translate both the local and the remote data accesses.
    2020
    21  * On the TSAR hardware platforms containing '''32-bit cores''', the physical address has 40 bits : the 8 MSB bits define the target cluster identifier CXY, and the 32 LSB bits define the local physical address LPA. On these architectures, the virtual address is 32 bits, and this virtual space is too small to map all the distributed KDATA[cxy] and KHEAP[cxy] physical segments. On these architectures, ALMOS-MKH kernel runs partially in physical addressing: the kernel code is still replicated in all clusters, and uses  the '''Instruction MMU''' to map the local kernel code copy in the kernel virtual space. But, for data accesses, the '''Data MMU'' is deactivated as soon as a core enters the kernel, and it is reactivated when it returns to user. To build a 40 bits physical address from a 32 bits pointer, ALMOS-MK uses a software controlable (TSAR-specific) register, containing a cluster identifier, that is concatened to the 32 bits pointer (in pseudo identity mapping). The default value for this register is the local cluster identifier, and is used to access the local physical memory. To access physical memory in a remote cluster, the ''remote_read'' and ''remote_write'' primitives modify the extension register before the remote memory access, and restore it after the remote memory access.
     21 * On the TSAR hardware platforms containing '''32-bit cores''', the physical address has 40 bits : the 8 MSB bits define the target cluster identifier CXY, and the 32 LSB bits define the local physical address LPA. On these architectures, the virtual address is 32 bits, and this virtual space is too small to map all the distributed KDATA[cxy] and KHEAP[cxy] physical segments. On these architectures, ALMOS-MKH kernel runs partially in physical addressing: the kernel code is still replicated in all clusters, and uses  the '''Instruction MMU''' to map the local kernel code copy in the kernel virtual space. But, for data accesses, the '''Data MMU''' is deactivated as soon as a core enters the kernel, and it is reactivated when it returns to user. To build a 40 bits physical address from a 32 bits pointer, ALMOS-MK uses a software controlable (TSAR-specific) register, containing a cluster identifier, that is concatened to the 32 bits pointer (in pseudo identity mapping). The default value for this register is the local cluster identifier, and is used to access the local physical memory. To access physical memory in a remote cluster, the ''remote_read'' and ''remote_write'' primitives modify the extension register before the remote memory access, and restore it after the remote memory access.
    2222
    2323In both cases, communications between kernel instances are therefore implemented by a mix of RPCs (on the client / server model), and direct access to remote memory (when this is useful for performance). This hybrid approach is the main originality of ALMOS-MKH.