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Message-ID: <b88e1f4f-1e85-46ca-b317-d8e10fe894a3@amd.com>
Date: Fri, 29 Sep 2023 10:40:19 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Avadhut Naik <avadhut.naik@....com>, rafael@...nel.org,
lenb@...nel.org, linux-acpi@...r.kernel.org
Cc: yazen.ghannam@....com, linux-kernel@...r.kernel.org,
avadnaik@....com
Subject: Re: [PATCH] ACPI: APEI: Skip initialization of GHES_ASSIST structures
for Machine Check Architecture
On 9/28/23 2:42 PM, Avadhut Naik wrote:
> To support GHES_ASSIST on Machine Check Architecture (MCA) error sources,
> a set of GHES structures is provided by the system firmware for each MCA
> error source. Each of these sets consists of a GHES structure for each MCA
> bank on each logical CPU, with all structures of a set sharing a common
> Related Source ID, equal to the Source ID of one of the MCA error source
> structures.[1] On SOCs with large core counts, this typically equates to
> tens of thousands of GHES_ASSIST structures for MCA under
> "/sys/bus/platform/drivers/GHES".
>
> Support for GHES_ASSIST however, hasn't been implemented in the kernel. As
> such, the information provided through these structures is not consumed by
> Linux. Moreover, these GHES_ASSIST structures for MCA, which are supposed
> to provide supplemental information in context of an error reported by
> hardware, are setup as independent error sources by the kernel during HEST
> initialization.
>
> Additionally, if the Type field of the Notification structure, associated
> with these GHES_ASSIST structures for MCA, is set to Polled, the kernel
> sets up a timer for each individual structure. The duration of the timer
> is derived from the Poll Interval field of the Notification structure. On
> SOCs with high core counts, this will result in tens of thousands of
> timers expiring periodically causing unnecessary preemptions and wastage
> of CPU cycles. The problem will particularly intensify if Poll Interval
> duration is not sufficiently high.
>
> Since GHES_ASSIST support is not present in kernel, skip initialization
> of GHES_ASSIST structures for MCA to eliminate their performance impact.
>
> [1] ACPI specification 6.5, section 18.7
>
> Signed-off-by: Avadhut Naik <avadhut.naik@....com>
> ---
> drivers/acpi/apei/hest.c | 49 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 49 insertions(+)
>
> diff --git a/drivers/acpi/apei/hest.c b/drivers/acpi/apei/hest.c
> index 6aef1ee5e1bd..03cb0ece4235 100644
> --- a/drivers/acpi/apei/hest.c
> +++ b/drivers/acpi/apei/hest.c
> @@ -37,6 +37,20 @@ EXPORT_SYMBOL_GPL(hest_disable);
>
> static struct acpi_table_hest *__read_mostly hest_tab;
>
> +/*
> + * Since GHES_ASSIST is not supported, skip initialization
> + * of GHES_ASSIST structures for MCA.
> + * During HEST parsing, detected MCA error sources are cached.
> + * Flags and Source Id fields from these cached values are
> + * then referred to determine if the encountered GHES_ASSIST
> + * structure should be initialized.
> + */
> +static struct {
> + struct acpi_hest_ia_corrected *cmc;
> + struct acpi_hest_ia_machine_check *mc;
> + struct acpi_hest_ia_deferred_check *dmc;
> +} mces;
> +
> static const int hest_esrc_len_tab[ACPI_HEST_TYPE_RESERVED] = {
> [ACPI_HEST_TYPE_IA32_CHECK] = -1, /* need further calculation */
> [ACPI_HEST_TYPE_IA32_CORRECTED_CHECK] = -1,
> @@ -70,22 +84,53 @@ static int hest_esrc_len(struct acpi_hest_header *hest_hdr)
> cmc = (struct acpi_hest_ia_corrected *)hest_hdr;
> len = sizeof(*cmc) + cmc->num_hardware_banks *
> sizeof(struct acpi_hest_ia_error_bank);
> + mces.cmc = cmc;
> } else if (hest_type == ACPI_HEST_TYPE_IA32_CHECK) {
> struct acpi_hest_ia_machine_check *mc;
> mc = (struct acpi_hest_ia_machine_check *)hest_hdr;
> len = sizeof(*mc) + mc->num_hardware_banks *
> sizeof(struct acpi_hest_ia_error_bank);
> + mces.mc = mc;
> } else if (hest_type == ACPI_HEST_TYPE_IA32_DEFERRED_CHECK) {
> struct acpi_hest_ia_deferred_check *mc;
> mc = (struct acpi_hest_ia_deferred_check *)hest_hdr;
> len = sizeof(*mc) + mc->num_hardware_banks *
> sizeof(struct acpi_hest_ia_error_bank);
> + mces.dmc = mc;
> }
> BUG_ON(len == -1);
>
> return len;
> };
>
> +/* GHES and GHESv2 structures share the same format, starting from
Please follow the general kernel multi-line comment style here.
> + * Source Id and ending in Error Status Block Length (inclusive).
> + */
> +static bool is_ghes_assist_struct(struct acpi_hest_header *hest_hdr)
> +{
> + struct acpi_hest_generic *ghes;
> + u16 related_source_id;
> +
> + if (hest_hdr->type != ACPI_HEST_TYPE_GENERIC_ERROR &&
> + hest_hdr->type != ACPI_HEST_TYPE_GENERIC_ERROR_V2)
> + return false;
> +
> + ghes = (struct acpi_hest_generic *)hest_hdr;
> + related_source_id = ghes->related_source_id;
> +
> + if (mces.cmc && mces.cmc->flags & ACPI_HEST_GHES_ASSIST &&
> + related_source_id == mces.cmc->header.source_id)
IMO, there should be parentheses around statements with multiple terms
to improve clarity.
if (mces.cmc && (mces.cmc->flags & ACPI_HEST_GHES_ASSIST) &&
(related_source_id == mces.cmc->header.source_id))
> + return true;
> + else if (mces.dmc && mces.dmc->flags & ACPI_HEST_GHES_ASSIST &&
The "else" is not needed, because of the return.
IOW, use "else if" when you want to skip a check if the previous "if"
was true. Here the check is already skipped if the previous "if" was
true and did a return.
Also, the order of the types is "cmc, mc, dmc" in the struct definition
and hest_esrc_len(). But here it is "cmc, dmc, mc". This is just a minor
nit about consistency in ordering.
> + related_source_id == mces.dmc->header.source_id)
> + return true;
> + else if (mces.mc && mces.mc->flags & ACPI_HEST_GHES_ASSIST &&
> + related_source_id == mces.mc->header.source_id)
> + return true;
> +
> + return false;
> +}
> +
> typedef int (*apei_hest_func_t)(struct acpi_hest_header *hest_hdr, void *data);
>
> static int apei_hest_parse(apei_hest_func_t func, void *data)
> @@ -113,6 +158,10 @@ static int apei_hest_parse(apei_hest_func_t func, void *data)
> hest_hdr->source_id);
> return -EINVAL;
> }
Newline here please.
> + if (is_ghes_assist_struct(hest_hdr)) {
> + hest_hdr = (void *)hest_hdr + len;
> + continue;
> + }
>
> rc = func(hest_hdr, data);
> if (rc)
Besides the minor formatting comments, this looks good to me.
Reviewed-by: Yazen Ghannam <yazen.ghannam@....com>
Thanks,
Yazen
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