linux-kernel - Re: [PATCH v6 14/17] powerpc: Add support for setting SPRN

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Message-ID: <1502749503.4493.34.camel@kernel.crashing.org>
Date:   Tue, 15 Aug 2017 08:25:03 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     mikey@...ling.org, stewart@...ux.vnet.ibm.com, apopple@....ibm.com,
        hbabu@...ibm.com, oohall@...il.com, linuxppc-dev@...abs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 14/17] powerpc: Add support for setting SPRN_TIDR

On Mon, 2017-08-14 at 13:03 -0700, Sukadev Bhattiprolu wrote:
> As Ben pointed out, we are going to be have limit the number of TIDs (to
> be within the size limits), so we won't be able to use task_pid_nr()? But
> if we assign the TIDs in the RX_WIN_OPEN ioctl, then only the FTW processes
> will need the TIDR value.

But you'll have to assign it for all present and future threads of that
process which is somewhat hard to do without races.

> Can we then assign new, globally-unique TID values for now and have the ioctl
> fail with -EAGAIN if all TIDs are in use? We can extend to per-process TID
> values, later?

Why would you want to do that ?

Ben.