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Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Lynn Wheeler Newsgroups: comp.arch Subject: Re: Is Parallel Programming Hard, And, If So, What Can You Do About It? Date: Tue, 20 May 2025 16:38:31 -1000 Organization: Wheeler&Wheeler Lines: 59 Message-ID: <877c2awuvs.fsf@localhost> References: <0ec5d195f4732e6c92da77b7e2fa986d@www.novabbs.org> <2025May13.094035@mips.complang.tuwien.ac.at> <1000nfp$2440u$1@dont-email.me> <1000pae$3uvs3$3@dont-email.me> <100bdhq$lhdb$3@dont-email.me> <87sel1jw9z.fsf@localhost> <100e28i$11n5t$1@dont-email.me> <100g5an$1q32t$1@dont-email.me> <100g9ip$1otvf$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain Injection-Date: Wed, 21 May 2025 04:38:35 +0200 (CEST) Injection-Info: dont-email.me; posting-host="430801cc2a2d3bee3c2e3eabbda887fb"; logging-data="2787562"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19atS4zdl6Ydb38V2XJaOpR41LtZwLkiMs=" User-Agent: Gnus/5.13 (Gnus v5.13) Cancel-Lock: sha1:sRu9hKp+2vYc0S9M0UKAH3meXsc= sha1:Z76S5/uTamH0GAHzFtuLgElRJr0= Bytes: 5064 Stephen Fuld writes: > I presume you know that the 3880 controller did not do what today we > call command queuing, so I think you were referring to a potential > queue in the host. That being the case, the controller doesn't know > if there is a queue or not. So given that, why not start reading > record 1 on the next track. If a request comes in, you can abandon > the read to service the request - no harm, no foul. If there isn't, > and you subsequently get a request for that track, it's a big win. > The only potential loss is if you get a request for the track that was > LRU and got pushed out of the cache. over optimizing full track read ahead could lock out other tasks that had competing requirements for other parts of the disk. trivia: early 70s, IBM decided to add virtual memory to all 370s. Early last decade I was asked to tract down the decsion. I found staff member to executive making the decision. Basically MVT (IBM's high end, major batch system) storage management was so bad that (multiprogramming) region sizes had to be specified four times larger than used, as a result typical (high-end) 1mbyte 370/165 only ran four regions concurrently, insufficient to keep system busy and justified. Running MVT in a 16mbyte virtual address space (sort of like running MVT in CP67 16mbyte virtual machine) would allow concurrent regions to be increased by factor of four times (caped at 15 because of 4bit storage protect key) with little or no paging. Later as high-end systems got larger, they needed more than 15 concurrent running regions ... and so switched from VS2/SVS (single 16mbyte virtual address space) to VS2/MVS (a separate 16mbyte virtual address space for each "region", went through MVT->VS2/SVS->VS2/MVS) along the way, I had been pontificating that DASD (disks) relative system throughput has been decreasing ... in 1st part of 80s, I turned out analysis that in the 15yr period since the IBM 360 1st ships, DASD/disk relative system throughput had declined by an order of magnitude (i.e. DASD got 4-5 times faster while systems got 40-50 times faster). Some DASD division executive took exception and assigned the division performance group to refute the claim ... after a few weeks, they came back and bascially said I had slightly understated the issue. The performance group then respun the analysis for user group presenation on how to configure disks and filesystem to improve system throughput (SHARE63, B874, 16Aug1984). 1970 IBM 2305 fixed-head disk controller supported 8 separate psuedo device addresses ("multiple exposure") for each 2305 disk ... each having channel program that the controller could optimize. In 1975, I was asked to help enhance low-end 370 that had integrated channels and integrated device controllers ... and I wanted to upgrade microcode so I just update a queue of channel programs that the (integrated microcode) controller could optimize (wasn't allowed to ship the product). Later I wanted to add "multiple exposure" support to 3830 (precursor to the 3880) for 3350 (moveable arm) disks (IBM east coast group was working on emulated electronic memory disks, considered it might compete and got it vetoed. sometime later they got shutdown, they were told IBM was selling all electronic memory it could make as higher markup processor memory). -- virtualization experience starting Jan1968, online at home since Mar1970