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    SubjectRe: Slow pthread_create() under high load
    Hi,

    On Mon, Mar 27, 2000 at 02:16:08PM +0200, Joerg Pommnitz wrote:
    >
    > > Maybe, but although a lot of the POSIX threads are reasonable, things
    > > like requiring uid/gid updates to be instantly effective across all
    > > threads in the process are just insane. There ain't no way that's
    > > going into the kernel any time soon: it would require adding
    > semaphore
    > > locking to all of the credential information that is currently task-
    > > local.
    >
    > Isn't this more the case of a missing "CLONE_CREDENTIALS" flag?

    No. That's the whole point: we have per-task credentials. If we
    went instead to have per-process credentials, with credentials shared
    amongst all tasks, then every syscall which uses permissions would
    have to lock the credentials structure while it is running, or risk
    having credentials changing in the middle of a syscall. That's why
    CLONE_CREDENTIALS would have to add a bucket of extra, slow, locking
    all over the kernel. No thanks, if it can be done in user space
    (which it can, albeit not very efficiently when we do a process-wide
    setreuid).

    > If POSIX specifies that credential are shared among threads
    > (similiar to VM, files,...) and Linux does not do this, than
    > it's not the specification that is broken but Linux' implementation
    > of the same...

    No, because Linux has never claimed to implement that bit of POSIX.
    It implements something much more sane instead.

    --Stephen

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