From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: "nathanl@linux.ibm.com" <nathanl@linux.ibm.com>
Cc: Tyrel Datwyler <tyreld@linux.ibm.com>,
Nick Child <nnac123@linux.ibm.com>,
Andrew Donnellan <ajd@linux.ibm.com>,
Scott Cheloha <cheloha@linux.ibm.com>,
Nicholas Piggin <npiggin@gmail.com>,
Laurent Dufour <ldufour@linux.ibm.com>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH 8/8] powerpc/rtas: consume retry statuses in sys_rtas()
Date: Thu, 25 Jan 2024 15:55:09 +0000 [thread overview]
Message-ID: <33ca48b8-f847-4d2b-b95f-741f0e082d2d@csgroup.eu> (raw)
In-Reply-To: <20230220-rtas-queue-for-6-4-v1-8-010e4416f13f@linux.ibm.com>
Hi Nathan,
Le 06/03/2023 à 22:33, Nathan Lynch via B4 Relay a écrit :
> From: Nathan Lynch <nathanl@linux.ibm.com>
>
> The kernel can handle retrying RTAS function calls in response to
> -2/990x in the sys_rtas() handler instead of relaying the intermediate
> status to user space.
From this series with still have patches 5, 7 and 8 awaiting in
patchwork, see
https://patchwork.ozlabs.org/project/linuxppc-dev/list/?submitter=85747
and patch 8 doesn't apply anymore.
Are those 3 patches still relevant or should they be discarded ?
Thanks
Christophe
>
> Justifications:
>
> * Currently it's nondeterministic and quite variable in practice
> whether a retry status is returned for any given invocation of
> sys_rtas(). Therefore user space code cannot be expecting a retry
> result without already being broken.
>
> * This tends to significantly reduce the total number of system calls
> issued by programs such as drmgr which make use of sys_rtas(),
> improving the experience of tracing and debugging such
> programs. This is the main motivation for me: I think this change
> will make it easier for us to characterize current sys_rtas() use
> cases as we move them to other interfaces over time.
>
> * It reduces the number of opportunities for user space to leave
> complex operations, such as those associated with DLPAR, incomplete
> and diffcult to recover.
>
> * We can expect performance improvements for existing sys_rtas()
> users, not only because of overall reduction in the number of system
> calls issued, but also due to the better handling of -2/990x in the
> kernel. For example, librtas still sleeps for 1ms on -2, which is
> completely unnecessary.
>
> Performance differences for PHB add and remove on a small P10 PowerVM
> partition are included below. For add, elapsed time is slightly
> reduced. For remove, there are more significant improvements: the
> number of context switches is reduced by an order of magnitude, and
> elapsed time is reduced by over half.
>
> (- before, + after):
>
> Performance counter stats for 'drmgr -c phb -a -s PHB 23' (5 runs):
>
> - 1,847.58 msec task-clock # 0.135 CPUs utilized ( +- 14.15% )
> - 10,867 cs # 9.800 K/sec ( +- 14.14% )
> + 1,901.15 msec task-clock # 0.148 CPUs utilized ( +- 14.13% )
> + 10,451 cs # 9.158 K/sec ( +- 14.14% )
>
> - 13.656557 +- 0.000124 seconds time elapsed ( +- 0.00% )
> + 12.88080 +- 0.00404 seconds time elapsed ( +- 0.03% )
>
> Performance counter stats for 'drmgr -c phb -r -s PHB 23' (5 runs):
>
> - 1,473.75 msec task-clock # 0.092 CPUs utilized ( +- 14.15% )
> - 2,652 cs # 3.000 K/sec ( +- 14.16% )
> + 1,444.55 msec task-clock # 0.221 CPUs utilized ( +- 14.14% )
> + 104 cs # 119.957 /sec ( +- 14.63% )
>
> - 15.99718 +- 0.00801 seconds time elapsed ( +- 0.05% )
> + 6.54256 +- 0.00830 seconds time elapsed ( +- 0.13% )
>
> Move the existing rtas_lock-guarded critical section in sys_rtas()
> into a conventional rtas_busy_delay()-based loop, returning to user
> space only when a final success or failure result is available.
>
> Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
> ---
> arch/powerpc/kernel/rtas.c | 28 ++++++++++++++++------------
> 1 file changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index 47a2aa43d7d4..c330a22ccc70 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -1798,7 +1798,6 @@ static bool block_rtas_call(int token, int nargs,
> /* We assume to be passed big endian arguments */
> SYSCALL_DEFINE1(rtas, struct rtas_args __user *, uargs)
> {
> - struct pin_cookie cookie;
> struct rtas_args args;
> unsigned long flags;
> char *buff_copy, *errbuf = NULL;
> @@ -1866,20 +1865,25 @@ SYSCALL_DEFINE1(rtas, struct rtas_args __user *, uargs)
>
> buff_copy = get_errorlog_buffer();
>
> - raw_spin_lock_irqsave(&rtas_lock, flags);
> - cookie = lockdep_pin_lock(&rtas_lock);
> + do {
> + struct pin_cookie cookie;
>
> - rtas_args = args;
> - do_enter_rtas(&rtas_args);
> - args = rtas_args;
> + raw_spin_lock_irqsave(&rtas_lock, flags);
> + cookie = lockdep_pin_lock(&rtas_lock);
>
> - /* A -1 return code indicates that the last command couldn't
> - be completed due to a hardware error. */
> - if (be32_to_cpu(args.rets[0]) == -1)
> - errbuf = __fetch_rtas_last_error(buff_copy);
> + rtas_args = args;
> + do_enter_rtas(&rtas_args);
> + args = rtas_args;
>
> - lockdep_unpin_lock(&rtas_lock, cookie);
> - raw_spin_unlock_irqrestore(&rtas_lock, flags);
> + /*
> + * Handle error record retrieval before releasing the lock.
> + */
> + if (be32_to_cpu(args.rets[0]) == -1)
> + errbuf = __fetch_rtas_last_error(buff_copy);
> +
> + lockdep_unpin_lock(&rtas_lock, cookie);
> + raw_spin_unlock_irqrestore(&rtas_lock, flags);
> + } while (rtas_busy_delay(be32_to_cpu(args.rets[0])));
>
> if (buff_copy) {
> if (errbuf)
>
next prev parent reply other threads:[~2024-01-25 15:56 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 21:33 [PATCH 0/8] RTAS changes for 6.4 Nathan Lynch via B4 Relay
2023-03-06 21:33 ` Nathan Lynch
2023-03-06 21:33 ` [PATCH 1/8] powerpc/rtas: ensure 8-byte alignment for struct rtas_args Nathan Lynch
2023-03-06 21:33 ` Nathan Lynch via B4 Relay
2023-03-23 4:00 ` Andrew Donnellan
2023-03-06 21:33 ` [PATCH 2/8] powerpc/rtas: use memmove for potentially overlapping buffer copy Nathan Lynch
2023-03-06 21:33 ` Nathan Lynch via B4 Relay
2023-03-23 4:09 ` Andrew Donnellan
2023-03-06 21:33 ` [PATCH 3/8] powerpc/rtas: rtas_call_unlocked() kerneldoc Nathan Lynch via B4 Relay
2023-03-06 21:33 ` Nathan Lynch
2023-03-23 4:15 ` Andrew Donnellan
2023-03-06 21:33 ` [PATCH 4/8] powerpc/rtas: fix miswording in rtas_function kerneldoc Nathan Lynch via B4 Relay
2023-03-06 21:33 ` Nathan Lynch
2023-03-23 0:17 ` Andrew Donnellan
2023-03-06 21:33 ` [PATCH 5/8] powerpc/rtas: rename va_rtas_call_unlocked() to va_rtas_call() Nathan Lynch
2023-03-06 21:33 ` Nathan Lynch via B4 Relay
2023-03-23 4:17 ` Andrew Donnellan
2023-03-23 16:11 ` Nathan Lynch
2023-03-29 12:24 ` Michael Ellerman
2023-03-06 21:33 ` [PATCH 6/8] powerpc/rtas: lockdep annotations Nathan Lynch
2023-03-06 21:33 ` Nathan Lynch via B4 Relay
2023-03-23 6:01 ` Andrew Donnellan
2023-03-06 21:33 ` [PATCH 7/8] powerpc/rtas: warn on unsafe argument to rtas_call_unlocked() Nathan Lynch via B4 Relay
2023-03-06 21:33 ` Nathan Lynch
2023-03-23 4:25 ` Andrew Donnellan
2023-03-23 12:17 ` Nathan Lynch
2023-03-24 0:56 ` Nathan Lynch
2023-03-29 12:20 ` Michael Ellerman
2023-03-29 16:23 ` Nathan Lynch
2023-03-06 21:33 ` [PATCH 8/8] powerpc/rtas: consume retry statuses in sys_rtas() Nathan Lynch via B4 Relay
2023-03-06 21:33 ` Nathan Lynch
2023-03-23 6:26 ` Andrew Donnellan
2023-03-23 19:39 ` Nathan Lynch
2023-03-23 9:44 ` Michael Ellerman
2023-03-23 13:40 ` Nathan Lynch
2024-01-25 15:55 ` Christophe Leroy [this message]
2024-01-25 16:33 ` Nathan Lynch
2024-01-25 16:46 ` Christophe Leroy
2024-01-25 17:23 ` Nathan Lynch
2023-04-06 1:09 ` (subset) [PATCH 0/8] RTAS changes for 6.4 Michael Ellerman
2023-04-26 12:12 ` Michael Ellerman
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