11/3/2022 0 Comments Kernel retrieve timeslice usedUnfortunately, many such systems are ill-suited to the low-latency and predictable timing requirements of real-time applications. Since it involves moving the stack (and thus changing the addresses of everything that's on the stack), it's probably not doable for C/C++.In order to eliminate the costs of proprietary systems and special purpose hardware, many real-time and embedded computing platforms are being built on commodity operating systems and generic hardware. Kernel retrieve timeslice used code#I'm not sure how hard it would be to get it working in the kernel, but at a glance it looks non-trivial: the implementation depends on -fuse-ld=gold, which doesn't work with the kernel the generated code uses the _private_ss slot in the %gs/ %fs TCB, which would presumably have to change to access something in task_struct *current instead and _morestack uses mmap to allocate new stack segments, which won't work (and there isn't one obvious way to safely allocate memory in kernel context).įor Go, split stacks were problematic (performance-wise) and 1.3 will switch to reallocating contiguous stacks. GCC -fsplit-stacks works for C/C++ code in user-space now, at least on i386/x86_64 Linux. Posted 18:57 UTC (Wed) by dtlin (subscriber, #36537) it'd also be easy to implement lazy page allocation for kstacks further reducing their memory consumption (let's face it, many kstacks will never actually make use of the whole 16k yet they'll always have to be fully allocated in the current scheme). the vmalloc ranges in a workload.Īnother advantage is that vmalloc by its nature handles lowmem fragmentation much better which becomes even more important now that amd64 kstacks have become order-2 allocations. i think in practice it'll come down to how many accesses are made to lowmem vs. the net performance impact depends on how the TLBs for each page size are organized in a given CPU and the access pattern of the virtual memory mapped by those entries (e.g., if there're separate TLBs for each page size and the access pattern continuously exhausts one but no the other(s) then obviously freeing/taking up extra entries will have a net positive/negative impact). as for its TLB impact, it's a tradeoff between one 2MB (or 1GB) TLB entry and 1-4 4k entries. Often occur with the XFS filesystem, which happens to be a bit moreĬorrect but note that the lowmem map will keep using 2M/1G pages. But he seems to be nearly alone in thatĭave Chinner often has to deal with stack overflow problems, since they Such proposals have seen resistance before, and that happened this time Proposing that it was time to double the stack size on x86-64 to 16KB. Out to be a stack overflow he responded by Recently, Minchan Kim tracked down a crash that turned Increasingly, it seems, those call chains don't even fit into an 8KB stack Modern kernels can end up creating surprisingly deep call chains that just Stack to 4KB, but that effort eventually proved to be unrealistic. As recently asĢ008 some developers were trying to shrink the Has been put into an 8KB allocation - two physical pages. To keep the size of the kernel stack small.įor most of the history of Linux, on most architectures, the kernel stack These concerns have always provided a strong motivation The stack must be physically contiguous can stress the memory management In the system, the space taken for kernel stacks can add up the fact that SinceĮvery process could conceivably be running in the kernel at the same time,Įach must have its own kernel stack area. Memory required for each process is a place to put the kernel stack. Though it may seem small, one of the more important pieces of Every process in the system occupies a certain amount of memory just byĮxisting.
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